Is there a rule for removing spam with random alphanumeric characters?

Hi,

I'm a new mod of r/mommit that joined to clean the chronic spam up. I know essentially nothing about programming, coding, or operating bots, but with the help of the excellent library you have here on the sidebar, I've gotten a few rules into place that seem to help. However, we're still having problems with spam coming from all sorts of sites, but having a commonality of using random alphanumeric characters like RhGI2tsF at the end. I don't see any pre-written rules in the library or by searching old threads that address this ad have basically no hope of being able to do it myself. Can anyone offer help?

Thank you.