What is H)4H!e

My error logs often show failed requests for “H)4H!e” and “ABu+ AKV2P %*D1”. I have no idea what these mean, my best guess is that they are some kind of hacking attempt. Does anyone know anything about these strange strings?

As far as I know my site is healthy, but now I’m worried that I might be open to some kind of attack I don’t understand.