Well silly, if you identify all the teams in the same platoon with a unique marking you would know right?
I have seen some folks use common terrain (rubble, street, grass, mud, etc...) to mark platoons. I have even seen bushes/rocks in common locations like a corner to mark a platoon. All of 1st Platoon have a bush in the lower right hand corner.
Tanks give you another way to mark that is historical...by using that nations/unit you are modelling historic method. Like the Brits using circles, triangles and squares, Americans nicknaming their vehicles so all of A company has names that begin with "A"...and the old bumper number A-11 (1st tank, 1st Platoon, A co)
Since by now you know I am building a Brit Para force I don't have many Tanks to have to use that method. I instead prefer to use a color code marking system for my teams. I paint markings on the back of the base in 3 sections. The left most section IDs the Company, the center IDs the Platoon, and the right IDs the Squad. The Company section gets 1 stripe and the other 2 receive 2 little stripes. The Company Marking is reserved only for the Company Command Section (and that is the only marking they get), and Divisional Support Units, who would get markings in all 3 sections. Did this because of the Field Artillery Battery really.and I wanted to separate the 2 firing platoons from the Battery HQ and Staff Team. Also gives me more options if I expand to build a second Para company (Yay!!!! more Denison smocks to paint!)
A pictures are worth more than the words I types above so...
The Color Code System for my Brit Paras:
Now for some examples (you might have seen these before in my earlier posts and wondered what was going on):