I do find that signs with grammatical mistakes annoy me, as do those which are garbled and incoherent. Signs normally only contain a few words, so it is surely worth checking them before they are printed.
Somehow, one supermarket chain has managed to print signs showing us where to find 'Todays checkout captain'. They also offer 'Two hours free parking'. It would be nice if they tidied up their apostrophes a bit. Given the irritation such signs cause many people, establishing a company policy for a bit more accuracy would be good PR.
However, they are far from the worst offenders; some off-licences (shops selling alcohol) have a notice saying 'If you are lucky enough to look under 18 you will have to prove it.' Presumably, they mean that people over 18 who don't look their age will have to prove that they are old enough to buy alcohol. However, they have chosen a garbled message that seems to indicate the opposite of what they intend.