OWNER PROP hide from players

Blind shot since I don't have gmod nor DarkRP installed.

Just for a test, try the following:

1) Navigate to DarkRP/gamemode/modules/fpp/pp/client/hud.lua

2) Go to line 186, it shoul look like this:

if FPP.getPrivateSetting("HideOwner") then return end

3) Replace it with:

if FPP.getPrivateSetting("HideOwner") or !LocalPlayer():isAdmin() then return end

NOTE: This is just a test, you shouldn't modify DarkRP core files, but try it out and see if its works. If you update DarkRP, this change will be overwritten again, keep that in mind. A more elegant way could be to modify the HideOwner setting with an external addon, but I don't mess with that.

And how to make a check by groups or how to make isAdmin take into usergroups?

I guess it depends, what permission system are you using? ULX?

IsAdmin() should work with most admin mods, you could extend even it to IsSuperadmin().

But if you have custom groups (maybe 'Moderator') it depends on the mod.

I need for SAM

Just use GetUserGroup(). CAMI exists for this reason.

Is it possible to hide the inscription from the cars?

I'm not sure what you mean

To prevent the owner of the car from appearing on the screen

It's the same thing as what Momox posted. They both use the same thing if it's darkrp for cars and props.