I agree there are some similarities, but my general feeling is that they are by different people. The "M" and the "r" in particular are different, but the second one looks much more fluent to me - a greater slope, and narrower and slightly less careful letters.
However, you say they are from "certificates", and assuming these are from England or Wales, these do not always include the original signatures of the parties being married. The circumstances I can think of where you would see the original signature on a certificate are:
1. it comes from a local register office which incorporates a photocopy of the register
2. it was issued at the time of the marriage where the minister allowed the couples to sign it themselves, rather than copying the signatures himself
3. it was issued by the GRO, and the minister had (very unusually) asked the couple to sign the quarterly return form that is used by the GRO to compile their indexes, and sometimes incorporated in certificates
Case 1 is fairly common, but in cases 2 and 3 you might not be able to find out whether it had happened or not, though you might sometimes suspect it if the writing is very different from the rest of the entry.
So, can you confirm that these are copies of the actual signatures in the register?
Arthur
