now, i'm useless at grammer and spelling. but i was wondering what the real plural of viruses are (is?) when i sawed this on the street.

i think it probably is viruses rather than virii.

but on the other side of the sign it was missing the final 's'

having different spelling on each side suggests they created different versions from scratch. Someone should refer them to a computer centre to tell them they can use computers to avoid having to do such things (they even have speling detecters).