Grammar ninjas: pedants or unsung heroes?

OK quick survey.
In your place of study or business you see an 'official' looking sign with an obvious (to you anyway) punctuatio-grammatical error. for example:
"All cup's must be washed - It is not the cleaners job!!!"
Do you A)Probably not notice, and definitely not care,
B) Roll your eyes, grumble, and possibly make a sarcastic comment to an equally grammar aware colleague, or
C)Immediately pat your pockets in search of a sharpie, stickers and/or bottle of correction fluid to fix the offending notice?

If the answer is A) - why do you even READ this blog? Not that I'm discouraging you, but really, what's the attraction?
B)This response is pretty normal, I guess, and covers most people I know, but
C), ah C): these are my kindred, the grammar ninjas.

We're a shy and mostly passive aggressive breed. We rarely make ourselves known by vocally complaining, but left alone with an apostrophe free possessive and a marker, we really cannot be trusted. Some, like my friend Becky, will take no credit of any kind, painstakingly recreating the font, size and colour of the original text in order that her added punctuation should fade seamlessly in. The other approach is the '3 out of 10: please see me' approach. The angry, red scrawl which berates the sign maker by regressing them to their childhood English lessons. Missing punctuation and capital letters added, unnecessary letters scored through and sometimes even a teacherish comment at the bottom complaining about the lax standards of the establishment. This can be quite funny, and IMO, there's little excuse for errors in the signage of, say, an educational establishment, or any place of business that expects its employees to produce correctly spelled and punctuated work.
So maybe the discreet way of doing things is more tactful, but less noticed by the people who could stand to learn a little more. The red pen method might offend but at least points out what was missing in the first place. The apostro-free culprits at Becky's workplace seem to think that a bizarre irl version of Microsoft Spelling and Grammar Check exists in their corridors, ready at any time to magically undo their illiteracy. Would making both our corrections and our scorn more apparent do more to persuade them of the joys of literacy, or simply offernd them into a follow-up sign saying something along the lines of 'NOTICE! Dont deface the sign's?', resulting in greater rifts between colleagues?
Maybe the answer is in the technology. Googlemail recently trialed an application called 'Beer Goggles'. If you send an email late at night it makes you do long multiplication to prove that you're not drunkenly sending anything you'll regret. Perhaps a similar application could pop up before office workers are allowed near the printer. If you can't pass a simple grammar test, to don't get to hit print. It would make all of us pedants so much calmer...