Different use of the word "form." "Make" is one definition. Reba was referring to a form like a Social Security form, something to fill out. That is signed with the Fs as described.
I believe the use of that sign for "forum" is due to a mixup between the words "forum" and "form" as they sound almost exactly alike even to hearing people. It is not really conceptually accurate to an Internet forum.
On the other hand I don't know what the real sign is, if there is one. I would fingerspell it myself, with expansion if necessary. The only related sign I do know is BLOG.
