While this is true he does finger guns a lot, the very specific thumb to forehead to make an L pose, plus his expression, is unquestionably at the very least a concern. And given the rest of this series, I don't put much stock in "oh it's just a coincidence". The writing has made it clear that there's no such thing as that. The noumu with wings was Deku's old school bully and the doctor he met as a kid works for All For One to make noumu. Nothing just happens for no reason. Sometimes it's a silly overblown thing because Deku doesn't know how to write in his journal without sounding intense and we get Aoyama's little mini-arc... but other times we do get some legitimate Stuff, that we're expected to have paid attention to.
Because for some hand based reason, the Liberation Army might be feeling a bit more emboldened, and he might be intending to show his true colours soon. Or you know, he's proud and doing it even though no one will get it. Or, not to be TOO conspiracy theory since I don't buy this one at all, but I mean Mt Lady suddenly being motivated sure is A Thing to consider.
But yeah, look, I... look at Kaminari's expression too when he does it. That's not his normal look at all.