How? I tried to find anything but cant. I suspect i need a specific amoutn of posts until i can have a signature.

Welcome you to the forum.

Can you let me know why do you need a signature, please.

You need to be a Junior member at least to have rights of wearing signature but with that rank, without hyperlink.
Forum ranks/positions/badges (What do those shiny coins under my name mean?)
FAQ: Everything you need to know about forum 'activity, account ranks and merit

You can buy a Copper membership to have rights as almost same as Member rank. With Copper membership you can wear signature with hyperlinks. Click here to get details, costs and guides to buy it: https://bitcointalk.org/index.php?action=credit;promote

you need a reason for that? If so, why?

idaeriks