Yup, just a liquid sealer that has hardened.
If you go with the auto silicone sealers, the black stuff from Permabond is known to work (I used it as I wanted it to match the black paint). You can also buy a small tube of it which is more than enough to do the plug and the head cover seal up job.
Some use red silicone sealants (shows up ugly on assembled engine) and some use copper (higher temp, unnecessary except on exhaust gaskets and shows up on engine like red does)
Hondabond, Kawasakibond etc are silver, and your engine is black, right?
If you head is silver, pick a silver sealant by all means.
But if she is black, go with black ...