Yes, an apostrophe is a punctuation mark used to indicate either possession or contraction in writing.

apostrophe

The contraction of we had is we'd.
The apostrophe is the little superscript punctuation mark between the e and the d.

Additional answer
It's not correct to ask 'what is the apostrophe of we had'. It should be 'what is the contraction of we had'. The apostrophe is a punctuation mark that (amongst other things) denotes that a letter has been removed.

An apostrophe is something that can be used as a contraction or even a name (e.g)Tom's pencil

An apostrophe.