So you're saying when I see it I should be thinking "omfg, dw intercepted a sudden attack of the melissa virus!" ?? oh, well, I feel so much safer now! /snark

hehe.

(no, seriously, what was wrong with just using a variation on the 'lock' image? a 'filter' is really just a subset of the locked-post/friends-only concept. honestly, if I were assigning icons, I'd argue more for a shield being related to the age-designation on posts, in the sense of "shielded from too-young eyeballs" or some such. although come to think of it, some kids are kinda like viruses...)