This icon looks like the Roblox logo stacked on the top left corner of Roblox player. Select the flag icon located next to a user' Roblox Support How to Report Security Exploits - Roblox Support
If you encounter users or websites promoting hacks, you should report them immediately using these official Roblox Support tools: How to Report Rule Violations - Roblox Support
: Even if you aren't immediately banned, Roblox monitors for suspicious activity and can invalidate any in-game items or currency gained through unfair means. How to Properly Report Violations