What do the exclamation marks with red borders mean on the Boston map?

Best Answer
An exclamation mark indicates the main story-line mission. Once you go there you'll see a marker and this will either start you on a new mission or it acts as a checkpoint if you are already in a mission.
I haven't played AC-3 but in the other games that icon indicated either a pickpocket or a courier. So you will have to chase the civilian clothed person who is running and grab him, default is shift key on PC. This will give you a reward of some kind and possibly increase notoriety. In case of pickpocketers doing this will help regain the money they stole from you.
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