GRO hold copies of register entries, not originals, which were copied out and submitted each quarter by the local registration offices. So you will not see original signatures of your ancestors/relatives.
A certificate is a certified copy of an entry, so even ordering that from the local office doesn't mean you will get to see the signatures either - most likely, the certificate will be handwritten by one of the staff, copying the information from the register entry.
You need to make sure they know it is the signatures you are interested in - they might consider photocopying the original entry to create the certificate (but is is difficult, and many registers are too fragile) or an alternative that is often used is for them to write out a certificate in the normal way, and then supply a tracing of the original signatures with it.
I would suggest that these days even tracing would be frowned on but there is a slight possibility of them taking a digital photograph of the signatures for you.
Cheers
Guy
