If you play solo, you might never know you have the tag. Download or VanillaHUD Plus from ModWorkshop. These mods force the game to display the "CHEATER" label on your own name in the inventory screen.
The eternal struggle of dealing with cheaters in Payday 2! I've got a step-by-step guide to help you determine if you have a cheater tag fix: payday 2 how to know if you have a cheater tag fix
If you want the tag and play legit: