- They either age a lot faster (if normal) or more likely not at all (if enhanced by genetic technology, nanomachines, etc).
- They either speak with a heavy accent of something foreign and difficult to place, or they are the children of immigrants who difficult to place accents (in which case they were born here or brought here at a young age.
- When they initially arrive they will have trouble digesting the local food.
- They have above average intelligence and possibly physical attributes. Time travellers must be smart to be selected, and the future has had centuries of additional evolution to polish other qualities. Genetic engineering may also be commonplace in their eras, or they may be synthetic.
- They will tend to have an interest in history and social sciences, because these disciplines will study the past more than hard sciences.
- They rarely show up alone. Working in teams is the best way to avoid alienation and survive the psychological stress of existing in a completely foreign time and culture. Though there could be exceptions.
- Almost always more self-assured and confident than normal. At times possibly fearless due to knowing in advance what will probably happen.
- More likely to travel a lot.
- Are very patient people.
- They tend to be utilitarian or psychopathic, because they know how expendable you are (they can always time travel again and start over).
- Due to the Heisenberg Uncertainty Principle, they will not necessarily know exactly what actions you are going to take, but more likely what actions you have a statistical probability of doing. Similarly, they can only predict events as probabilities based on the collected statistics of previous time travelling or observation. The multiverse and/or their interaction with the universe allow for this universe to diverge from the universe that they come from.
The nature of reality, due to the Heisenberg Uncertainty Principle, is that events are not set in stone, but rather there are probabilities that any number of possible events will occur. Even if they are actually determined by cause and effect, we can never know enough to see that level of certainty.
Now what this means for time travellers is that they don't know with 100% certainty what will happen. They at best know the statistical probability of events as collected from previous time travelling observations. If they're lazy and haven't done that data collection, they will only have their own world's history, which will only give them some of the probable events, and without knowing how probable those events are of reoccurring. Though usually that map will still be fairly decent, since most probable events usually happen.
Even if they do know the probabilities, if you wanted to thwart them, you could attempt to intentionally do what seems improbable, or different from what you were originally planning to do. This might throw them off somewhat, but it will also make life difficult for you, because all the highly probable events are usually desirable ones like grocery shopping, etc. Eventually they can adapt to the new probability observations and then you'll be back at square one.
The bigger question is why would you want to fight the time travellers? The sheer amount of energy required to perform time travel (assuming it is even possible) means they would only do it for something really really important to them, unless energy becomes that cheap in the future that you get history tourists. Anyway, even having just a prior awareness of the probability of events is a huge advantage over you the average normal person, so there's no way you can win in the long run. Combined with their technology (assuming they brought it with them), they may as well be minor gods.
Time Traveller Protectorates
Occasionally a situation may occur that someone is important to the agenda of a time traveller. Perhaps they work for an organization meant to preserve the sanctity of the timeline, or they have plans for the life of a particular person. As a rule, time travellers do not reveal that they are protecting someone, even to that person, because otherwise, that person may become overconfident and take unnecessary risks. If you suspect that you are being protected by time travellers, do not attempt to test this theory by, say, jumping in front of a car. They are likely to stop protecting you then because they don’t want to be constantly tested or relied upon.
On the other hand, prayer to some deity can serve its uses to provide time travellers with mind reading technology some idea of your particular needs and desires. Whether or not they feel accommodating however is up to them.
Conservatives and Progressives
Time travellers generally come in two forms. Conservatives follow rules that try to maintain the original timeline and avoid making any effective changes. They can be tourists, historians, or guardians of the timeline, but they all share the fact that they won’t interfere except perhaps to counteract a Progressive time traveller's interference. Progressives on the other hand have some agenda to change the timeline in some way for some purpose. Usually it is to further the interests of some future civilization or faction, and they can be benign or malevolent depending on how you factor into their plans. They might support and protect you, or they may be there to kill you. They tend to intervene significantly more in the timeline and cause changes. They often come into conflict with Conservatives and other Progressives with different agendas. Interestingly, a time traveller may be Progressive on certain timelines, and Conservative on their desired optimal timeline.
Time Travellers vs. Sliders
Sliding technology that allows travel between parallel universes is significantly more advanced that just Time Travel technology. Basic Time Travel technology is more limited in where it can go. For instance, say a Time Traveller goes back in time and changes the past. By doing so, the Time Traveller creates a new world line. If they then travel back into the future, they will stay on that new world line and go to the future created by their actions. Actually, by travelling to that future point, they will automatically create another new world line in which they appear in that point. Thus, all basic time travel is technically creating branching universes or world lines.
However, a time traveller without sliding technology cannot return to the original world line from which they came. They are essentially trapped in the newly created world lines. To return to their actual original timeline requires sliding into that parallel universe. Therefore, the most powerful time travellers are generally sliders.
Note that if the time traveller is careful not to make significant changes to the timeline, they can often still return to a future which is similar enough to one that they originally came from, that it is for all intents and purposes identical. However what happens is not that they return to the original timeline, but again, they create a new universe in which they “return”. Thus, two parallel universes exist, one in which they “return” and another in which they do not. Thus, basic time travel often seems to have a very low return rate, but not because the time travellers disappear. It’s just that even if you make no changes to the timeline, you’ll only appear to return to the original world about 50% of the time, even less if you make changes and get stranded. Sliders do not suffer from this problem.