Create a shortcut to insert the frames separator for beamer documents

[Ehud Behar]

I want to create a shortcut to insert the short thin red line that 
separates frames when the document class is Beamer.

I know how to create shortcuts, I just don't know the name of the 
"function" that actually inserts this red line.

In the lyx file this red line is called "Separator plain".

If you really think of it, I don't know the function name because I also 
don't know how to insert it from the menus, so you are welcome to tell 
me how to do that as well.