For those interested, I'll also be asking this question on Christianity.SE and Mi Yodeya (with respect to those religions).
In recent rallies, protesting what is perceived as bigoted policies by president Donald Trump, several individuals who are not in fact Muslim and do not subscribe to the Islamic faith have claimed they are Muslim in a show of solidarity with the Muslim world.
Would a non-Muslim sin if he proclaimed himself a Muslim for the sake of solidarity?
While I generally understand that not subscribing to the faith in general is sinful, I'm curious about the act of proclaiming that you are an adherent when that is not true (I'm asking in particular about the sin of falsely claiming adherence to the faith, this should be understood as being a different or greater magnitude sin than simply violating any general rules about lying or telling falsehoods).