Stained rock

Wasn't sure where to ask this.

This rock was dug out of a drain 20+ years ago and left on the ditch with all the other rocks. It's the only one to have this reddish color. I'm assuming it's some kind of staining from Iron?

I'd come up with a story of a man that was beheaded on that rock for wearing muddy boots in the house, leaving a gate open or something similarly annoying as a warning to those who would commit such an offense.  Iron is what makes blood red after all...