It looks as thought the signature is on a white base. If so there are three possible methods to help photograph it,
1. Take a photo at a very shallow angle towards the sun or a bright light source so that the base reflects light but the signature will appear darker.
2. Lightly use a black texta across the signature which will hopefully leave it showing as white against the blackened base.
3. Get a darkish powder and lightly rub it across the signature so the groove is filled. Wope off excess - hopefully the signature is visible now.
Good luck with the photography.