My advice:
- Never give up on your own stuff! Make it as good as it can be, in grammar, style and content.
- Stop bothering about other peoples' stuff. I call this "stop the tut"! - and try to stop myself from tutting when I see bad spelling or grammar. English evolves :)
I found that once I let go of spelling errors in facebook posts, texts, email etc - let alone public signage or notices! - I enjoyed life more. I might have an occasional chuckle to myself about bad grammar on a sign, and if someone asks, I'll always try to help. But I don't correct them.