Many times staff in other countries do not realize that a signature slip has been printed. In any event the USA transaction networks no longer require signatures, and I do not think that absence will prevent a transaction from posting to your account.
While it is true that staff in chip-and-PIN locations sometimes don't realize that a signature slip has been printed (and some others try to be handwriting experts), I'll take my chances contesting DCC on a signature verified transaction over a contactless transaction with no verification required.