Doesn't matter where the picture is from, it doesn't change the fact that anyone browsing the NFL thread from a public place is going to look like they are surfing for some sort of gay Asian personals.
I get that is it safe for work, but doesn't mean it belongs. And it's obvious what you are doing, there hasn't been enough board drama for you lately so you decided to stir up shit. You are trying to either force the mods to make specific rules for all sigs so you cry about how these boards have become a nanny state, or you are going to force them to start disallowing sigs on a case-by-case basis and you get to start crying about how these boards have become a nazi state, or your shit is allowed to continue and people have to explain to their co-workers/friends what the fuck they are looking at if they happen to walk into their cubical or are sitting behind them at Starbucks.
I guess it is a win-win-win situation for you, but it is still stupid.