There is not a lot of information on this, and what I am about to share is incomplete.
Armoured companies typically use the standard tank markings as laid out in the Apocalypse 1st edition core rulebook. Unfortunately I do not have access to this at present, but the images below are from a White Dwarf article released alongside the (then new) sentinel kit and are in keeping with the Apocalypse guidance (they explictly reference it). Tanks are given a number corresponding to their position with the company- the command tank of the first company being number 10. The tank in the Image below is no. 14, which would make it the lead vehicle of squadron 2 of the first company. The third vehicle in squadron 3 of the 5th company would be no. 59 under this numbering convention. The 1st company has red and white stripes, the second yellow and black. The other company colours are in the Apocalypse book I don't have access to. Here it is painted on the turret, I am pretty sure I have seen the standard hull position for the stripes on a studio vehicle too.
You can also see the sentinel unit markings on two different vehicles- the triangular armour panel on the right is red with the vehicle number in white. It is unclear how this scales, or whether the colour changes for subsequent companies. However, scout companies are usually part of a larger regiment, so it will be rare to have more than one company in a single regiment. I suspect a second company would be yellow etc. The number presumably refers to the vehicle seniority within the company- 0 is probably the company command vehicle.
The next image is from Codex Armageddon and includes Chimera markings. I have a strong feeling there is a better source explaining these somewhere, but it appears to revolve around a variable two colour strip plus a number. I suspect the number is referencing a squad or platoon with the colours referencing company + platoon, or company or platoon alone.
I have never seen any infantry markings beyond the regimental badge, but I would think they'd match the chimera markings on the vehicle transporting them. I'd put these on the side of the helmet.