Asking them implies that saying no is a possible option. If you don't ask and they complain you can act like they're behaving strangely and unreasonably. If you

Asking them implies that saying no is a possible option. If you don't ask and they complain you can act like they're behaving strangely and unreasonably. If you've asked them for permission before you've sent them the signal that having a problem with you using the logo is not strange or unreasonable. By asking you're also bringing the fact that you're using their logo to their attention, which they might not otherwise notice.