Just for the record;
Servers can enable SD #15 from https://wiki.multitheftauto.com/wiki/Anti-cheat_guide for additional protection, because disabled driver signing can make cheating easier. If you're getting kicked for SD #15 SIGN, then a server has decided to do so.
DSE (driver signing enforcement) can have been turned off on your PC for various reasons, such as;
- Virus/malware infection (the virus can disable it, so it can better execute its malicious code)
- Manually by you, or due to a pre-modded Windows installation
- Custom drivers or software that require signing to be turned off. Avoid using modded drivers, use official ones, and then you can easily re-enable signing. Furthermore, using software that ships untrusted, custom drivers like that presents you with a broad security risk. Generally, serious software publishers (legit ones) don't need to do that.
Solution (how to fix it, so you won't get kicked on this particular server again):
open command prompt (cmd) "as Administrator" and enter the following commands:
BCDEDIT /set NOINTEGRITYCHECKS OFF
BCDEDIT /set TESTSIGNING OFF
Restart your PC, and it should be resolved.
If it's not resolved, this means re-enabling signing was unsuccessful, probably because something on your PC has (automatically, or in a short while) disabled driver signing again.
This is most likely the work of a virus or software running on your PC In the background, which detects that signing has been enabled (which would obstruct its malicious activities), and makes sure to turn it off again. If this happens, (you still get kicked for SD #15 SIGN after trying to enable signing using the above CMD commands) then run a full antivirus and malware scan and think of any untrusted (PUP) software running, or ask for help on a dedicated tech support forum such as https://www.bleepingcomputer.com/forums/
For anyone (like server owners) reading this and possibly getting suspicious of someone;
Please note that only around 0.5% of all MTA players worldwide have disabled driver signing; we still want to avoid discriminating people with modded drivers and virus infections by default, which is why SD #15 SIGN kicking is still optional. A lot of other anti-cheats always block it. We currently don't need to, because cheating on MTA is still virtually impossible (due to the general state of AC) even if they disabled signing on their PC. It's more of an "just in case" thing. You cannot derive if someone is cheating or not from the SD #15 status. If you block it however, you will barely make any casualties.