Buffs and Debuffs are pentagon shaped.
The buffs points upwards while the debuff points downward.

On top of that, Doom is black and red, doton is black, red and purple/pink at the top of the icon.

The shape + the colors should be enough to make the difference, unless you are about to pass out from exhaustion which in this case... Get some rest.
Other people also mentionned it, Doom is scripted and never appear at random, only selected random targets.