I just asked a friend astrologer who is also interested in symbolism what does upside down triangle means. The man said: "upside down triangle symbolises manifestation of power or rooting. Getting thought forms into manifestation, projection of thought into reality. Armies usually use chevron, but can be also like this"
Those are 2 triangles, one within the other. Maybe it has something to do with tetrahedrons, Star of David, conversion into 3 dimensional representation, and field concepts.
Here are explanations from two military experts (translated from Russian).
...As for the inverted triangles, the expert said that such signs usually indicate that the equipment belongs to a military unit.
For example, white circles are used by the "Brave" group of troops. And the triangles that presumably appeared on the armored vehicles between April and August, according to the expert, may refer to similar tactical symbols applied to their vehicles by the Pskov paratroopers.
Their vehicles bear similar inverted triangles, but with Roman numerals inscribed in them, Knutov said.
"Usually such symbols are used to indicate belonging to some military district, but it is difficult to say anything about this symbol," the expert concluded.
And this one:
Combat veteran, Captain of the First Rank of the Reserve Vasily Dandykin said that a new tactical symbol - a white inverted triangle - has been noticed on the military equipment of the Russian Armed Forces.
According to the military expert, in general, tactical signs can be used as passwords that change from time to time. They can also signify a particular military unit.
"I served in the Navy, and we constantly had tactical numbers on the ships changed, it could be 100, 120 and so on, it's the order of the day. So it's quite possible they could have done such a thing just based on a certain expediency. To change the signs, as passwords are changed to designate a particular connection," Dandykin said.
In addition, a former special forces officer, retired colonel Anatoliy Matviychuk, also said that the system of identification signs is developed by special services, and the symbols are changed depending on the need.
And here are some pictures with various signs on them.