Rocky Raab, Utah Roadway Trivia question

[TreeDoc]

I just made that trek up I-15 to I-70 on our route to Colorado and back. With you being a Utahan I figger'd you might know something about this.

The Freeway road signs leading towards Salt Lake City are marked with their highway number over what looks like a little beehive. Some "beehives" have little circles on the top and mny others don't. My buddy and I want to know what that little figure is.....a beehive? Do we need to know a special handshake to garner this information.

I found this Pic on the 'net.