no idea, i think the ones above a player in game refer to have far from your tier they are but no clue for the symbols on the player list in game.
In game, there are green and red marks above tanks. Some are triangles, some are squares, some are diamonds, some are 2 hash marks, some are 3 hash marks.
The triangles are tank destroyers. These tanks will be dark gray tank silhouettes in the team list on right/left sides of your screen during a match.
The squares are artilery. These tanks will be a red silhouette in the team list on the right/left.
The diamond is actually just a single hash mark, as you'll see below. These are classified as light tanks. These will be light gray silhouettes on the left/right.
The two-hash (diamond with a diagonal line down the middle) mark tanks are medium tanks and will also be light gray.
The three-hash (diamond with two diagonal lines) mark tanks are heavy tanks.
These marks do not indicate what tier they are. As an example, you can be in a tier 3 medium tank or a tier 3 light tank. You can also be in a tier 8 medium tank. The tier 8
medium will absolutely destroy a tier 5
heavy tank because it can still do damage, will have TONS of armor, and will be fast enough to run circles around a heavy.