Many times mail-signatures are an overhead in chain mails. There should be an option in the mail client to restrict the addition of signature only to new mails (and not when replying or forwarding a mail). This will reduce the length and size of the mail, increasing efficiency of the ...
there are different items for mail sigantures in iNotes and Notes - in my opinion it should be the same or synchronized
The inclusion of email signatures in to meeting invitations would greatly reduce the need to open a new memo, copy the default mail signature and paste it in to meeting invitations.
There are other ideas already regarding rich text signatures and multiple signature which I think could apply here ...