Well you've obviously got the url right, now all you have to do is paste it into your profile as vbcode to make it work as a link.
In your profile, add 'whatever your want to say' behind the string.
The code would look something like:
[ URL=https://forum.literotica.com/showthread.php?s=&postid=6123729#post6123729]link to my...[/URL]
once it's in your sig then it will look like (this should work like you want): link to my...
The trick I used here to show the code and then the link is a small difference in the first case. I left a bogus space after the first bracket. This lets you see the code, but you have to remove the space to make it work (like I did in the second case).