No, there is no event for flag detection. However, if you are colliding with these entities you can check if is(you,FLAG1) returns True or False. If there are many entities you want to check if the FLAG is set you can scan through all entities on the map via ent_next and check if the returned entity pointer has its FLAG set.

You will have to describe your problem more fully (possibly with an example) for the best solution to be recommended. It is possible that you can use one of the many EVENTS already defined; please see the Gamestudio Manual for all the possible EVENTS.