This Anon tends to believe these are National Guard Troops directed by Putin for Border control. Similar demarcation lines in Russia and USA over Military on domestic soil. If Crimea was recognized as part of the Russian Federation, The Z troops would be used to secure Crimea, Invasion Troops to rest of Ukrainian territory would be normal armed forces.
"There is a lot of discussion about the Z mark seen on the tanks of the Russian army. Significantly, the ‘Z’ attracted public attention when it was seen on the Russia-Ukraine border with thousands of Russian tanks, vehicles carrying armored personnel. Also this mark has now become quite popular in Russia. It is also being seen behind cars, on people’s T-shirts.
Kamil Galev, from the research group ‘The Wilson Center’, says about this that some people are linking the meaning of Z to Z Pobedi (for victory). At the same time, some believe that Zapad is interpreted as the West. However, other experts about the Z mark believe that the Russian army is using this mark to identify its vehicles. So that the soldiers do not have any mistake in identifying their vehicles.
At the same time, according to a report in the Telegraph, such a mark is used for Rosvardia Troops. It means Russian National Guard. This is different from the soldiers of the army. Every action of Rosvardia Troops is directly informed to President Vladimir Putin.
After weeks of speculation about it, the Russian Defense Ministry said on Sunday that it came from “Za”. Which is the first word of the Russian phrase “Za pobedu”, which means to win."
https://irshadgul.com/russia-ukraine-war-why-z-is-written-on-russian-tanks-what-is-the-meaning-of-this-symbol-know/