Where is the eM CLient signature file stored

I want to try to do more formatting of my signature by changing the HTML.
I am therefore looking for where the signature is stored on my drive to allow me to modify it with third party software.

I am sorry, it is not possible to modify your signatures by the way you suggested. But you can generate your signature externally and then paste the HTML code of it by right-click at signature text and choosing Insert-Html and paste the code there (all of it in signature creating or modifying window).