Sirius never fell in love with a muggleborn (well, I mean, he might have, but he's not known for it) so I don't think people will think that's what it means, just that we're all traitors to pureblood values, or something. But then your entry did mention loving people we're 'not supposed to,' so who knows what it will get people thinking about.

I don't know, on one hand it might be more convenient to have people just realise it rather than having to make some kind of announcement. But yes, he might like the option.