So we all noticed the similarity between Graves' hair and Grindelwald's, right?
This ends up being what Grindelwald does. When he takes someone's identity with Polyjuice, the first thing he does is give his new body his preferred haircut. When he inevitably escapes from MACUSA, he starts doing the same damn thing all over again. Eventually Aurors and wizarding governments start catching on, and Grindelwald can't figure out why he's getting caught so easily now. (Drawback is that once in a while the Aurors bring in some hapless wizard who just thought his hair would look cool like that.)
Bonus for real!Graves being incredibly offended that his coworkers didn't figure it out sooner. "How the hell didn't the haircut tip you off?!" "We just thought you were trying something new and didn't want to be rude."
Grindelwald, crack - the hair gives it away
This ends up being what Grindelwald does. When he takes someone's identity with Polyjuice, the first thing he does is give his new body his preferred haircut. When he inevitably escapes from MACUSA, he starts doing the same damn thing all over again. Eventually Aurors and wizarding governments start catching on, and Grindelwald can't figure out why he's getting caught so easily now. (Drawback is that once in a while the Aurors bring in some hapless wizard who just thought his hair would look cool like that.)
Bonus for real!Graves being incredibly offended that his coworkers didn't figure it out sooner. "How the hell didn't the haircut tip you off?!" "We just thought you were trying something new and didn't want to be rude."