Summertime, and the living is easy — or it will be whenever the long line of traffic starts moving again.

Keep your temper, and pass your time by deciphering the Colorado license plates of the cars stopped around yours. What do those letters on the left side of some license plates signify?

Colorado’s motor vehicles divisions offer more than 100 variants of designated license plates, from vanity plates to PRM. (No, that doesn’t mean “Prom,” it indicates a vehicle used for interstate commerce.) And hundreds of proposed personalized plates don’t make it past the censors, e.g. “STDMFN” and “PINCHE.”

There are alumni plates, military plates, legislation-approved special interest plates like “Respect Life” (recognizing the 1999 massacre at Columbine High School) or “Share the road” (with bicycles).

Others are more cryptic. MMS? INT? Horseless carriage?

Here’s a cheat sheet decoding some of those designations:

CCL: Commercial call letter, meaning the owner possesses a standard radio, FM or television FCC license

DMO: Dealer demo. Vehicle dealer plates

DPT: Depot. Vehicles being road-tested or moved for repair and refurbishing

FLT: Commercial fleet. Issued to the owner of 10 or more vehicles — a company car fleet, or trailers, truck tractors and SMM equipment

FTR and FTK: Farm tractor or Farm truck. Vehicles transporting raw agricultural products or livestock

GVT: Government. State-owned or -leased vehicle

GVW: Any truck weighing at least 16,001 pounds

INT: Dealer in transit or Dealer full use. Vehicles being transported to sell, auction or store

Honorary Consul: Vehicles owned by official representatives or official consuls of a foreign government

Horseless Carriage: Vehicles limited to driving to or from assemblies, parades and conventions

MFG: Manufacturer. Plates that can be used on any new vehicle owned by and titled in Colorado to the manufacturer

PRM, ATL and ATK: Apportioned plate. Vehicles licensed for interstate commerce

SCL: Amateur call letter. Owner possesses a valid amateur radio license issued by the Federal Communications Commission

SMM: Special mobile machine. Equipment driven or pulled over the public highways to a specific destination

SMX: SMM equipment that doesn’t conform to Colorado lighting requirements

TRK: Special-use truck. Examples: mobile medical vans, trash compactors, concrete trucks

TPR: Transporter. Dealers and government agencies, repossession agents, tow cars

TVW: Any tractor primarily used to pull trailers and semi-trailers

Source: Colorado Department of Revenue/Division of Motor Vehicles