[@Genni]

You have to keep in mind, that it would be a very difficult thing to 'check-up'. Three groups of synths currently exist:

Those whom were freed by the Railroad and weren't affected by the Institute 'kill-all' signal. Those whom escaped during the Brotherhood attack on the Institute. And those whom currently are bound and serving the Institute scientist on the surface.

Thus your either a Synth, whom suspects but has no way of checking it up. OR a group of Synths whom escaped the Institute and decided to take up raiding.

(If you were an Institute placed one, chances are you would have gone berserker on anybody close to you)