It really depends on how you intend to use it and whether it needs to work with Reader, so it will help if you can provide more information. A stamp can be used for this, or you can set up a signature appearance for use with digital signatures. The pencil tool can also be used if you want that sort of functionality.
First sign with your signature an Blank sheet of paper.
Scan the image with a scanner.
Save the file as a jpg or png (preferred). file save at 150 dpi (n what ever image editor you have).
Now open stamps feature in acrobat.
Locate the file you just created.
fix the size height and width.
Then move stamp position to proper location (on a Mac Laptop, you can use the up, down, left, right arrow keys to nudge the stamp to exact position on Desktop machine with extended keyboard use the Home keys usuall clustered spearately in inverted T pattern).
Yep you link in now fixed. what most likely happed is when you click on Link tool in the forum, when window open the http:// is already in the window. Most likely you clicked at the beginning of the http and pasted your link.
I always when this window open triple click on the http:// so everything is selected, then hit Delete (I use Mac - PC it would be backspace) so window is completely empty then I paste the link.
But I occasionally I let it happen myself.