Merch is a slang believed to have been originated from Chicago, Illinois. Merch means to put it on something, or to be able to provide factual evidence that something is what you’re claiming it to be. An example of merch would be ‘Merch it on my mama, I’m gonna bang this chick by next week.’. This slang is heavily used by those in the criminal world. Lil Jay, a rapper from Chicago, said the following in his song ‘Competition(Freestyle)' “On the I, I can merch that on Insane”.
Another definition for merch is merchandise. Though lots of people using this definition are referring to real merchandises, when criminals use it, they are usually talking about work they have with them or moving, such as drugs and other contraband.