WELCOME to the forum.
Do a "search" and you will find remarks on this issue. In the mean time.........
I'm no LEO, BUT, I myself had asked this question before on another forum which is actually run by MA. police. If a LEO see's what seems to be an imprint of a firearm, you better be prepared to be stopped and questioned and possibly arrested. I know what you're going to say, "but the gun is concealed". That was my argument also, but hey, They are the police and can do/say what they want. IF You think there is a case, then go for it. You'll probably be the first one to fight it. You will be told to pick out another line of clothing so there is no imprinting whatsoever. If it's a CC state you better make sure it is Concealed. You MAY luck out and get a LEO say even though there is an imprint it is Concealed, where you might get another LEO and say it isn't. It's up to You. I guarantee you though that probably 98% of the folks on here will tell you to get another wardrobe. The Other 2% will probably tell Me that I'm an asshole (don't matter to me, my Wife calls me that all the time) and don't know what I'm talking about. THEY are the ones who will get their face planted on the pavement when a cop spots their imprint.
The answer's I gave You were pretty much what I was told from MA. police just so you know. From what I gathered, there really isn't anything in writing stating if it's against the law or not.
Use your smarts, research, avoid Any and All confrontations with police if You can and do the right thing. Good luck