Merit sources are free to reveal their source amounts, though I think it may be a bit unwise. While it will eventually become obvious roughly what the source amounts are from the stats, there's a huge difference between showing up in a "list of probable merit sources" and having a quote out there of you basically saying "I'm a merit source, come beg me for merit, complain about every merit I send, and accuse me of being part of the anti-X/pro-Y conspiracy."
I've had very few people beg for Merit, and I've made it clear I'm a source for more than a year and a half now. The funny ones also ask if they can buy my account 
Accusations aren't really a problem either, I've seen only a few occasions in which someone questioned the Merit I sent, and although I know I don't have to explain myself, I don't mind doing so either.