When they suddenly focus on here and now…
Sagittarius is usually very busy with a lot of things. They have projects and they are travelling around the world whenever they can. It may be difficult to find the time to actually meet at all. Once you do meet it is going to be clear if they find you interesting in that way or not, just pay attention to if they seem to be on their way somewhere and restless or if they actually look deep in to your eyes with fascination. That fascinated look is the thing that indicates if there is more than friendship going on. Once they start to realise it themselves (may take some time for them to admit because they will have to adjust their busy schedule for you) then they may turn very shy which is not what they usually are. So shyness and fascination will be the signs to look out for with this adventurer.