What is the Dollar sign ("$") at the end of every line in Vim

:set nolist

will turn off special characters for the current buffer, such as tabs being presented as ^I and end of line characters showing up as $.

However, if it's doing that consistently when you run vim, you need to look into your .vimrc (or other startup file where applicable) and find out what's doing the set list that causes it.

Open ~/.vimrc and check its contents
If you see a line like this:

set list

It means, it will display $ in every line to mark the end of line.
Either remove it or use :set nolist command in the vi editor.