What does a patch with the ace of spades and the grim reaper mean?

There is much symbolism associated with death and the Ace of Spades playing card and the Grim Reaper are two such symbols. Being used together is merely redundancy.

A person wearing the Ace of Spades patch is suggesting to the knowledgeable viewer that the will fight to the death when ever provoked. If there are other images added it can suggest other meanings. Among gangs if the letter "M" or the numeral "13" ('M' is the thirteenth letter of the alphabet) is added in the imagery it may suggest that the wearer has murdered someone or uses and/or sells marijuana.