The first two show a glob of solder that would be better removed and the third one seems to have a small glob as well. All of them appear to have burned flux residue.
This is nothing to be too concerned about, but cleaning them off will make future soldering easier.
I would suggest getting something like a metal scourer like this:
The holder at left is just to keep it in one place.
Heat up each iron in turn and jab the tip into the metal "wool" several times, with a bit of twisting (just wrist movement) and you should see a lot of that crud get removed. I would then tin each tip with fresh solder and then do the jabbing exercise again to leave a thin coating of solder on the tip and little or no flux. Then set it aside to cool, ready for the future.
The metal wool idea is good in that it will scrape down the sides of the tip, but with not a lot of force as it will "give". This allows the excess molten solder to be removed with minimal damaging force, which is why you will need to jab several times.
One of the biggest advantages, though, is that the metal wool does not cause the massive thermal stress you get when using a wet sponge which can damage tips. It also means that the tip doesn't cool down after a cleaning pass during soldering.