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The sign accompanying the Descent Propulsion System engine. It reads

Lunar Module Descent Engine

The Lunar Module (LM) was a two-stage vehicle designed for space operations near and on the Moon, incapable of reentering the Earth's atmosphere. The descent stage is the lower unmanned portion of the LM. The engine could be gimballed six degrees in any direction in response to positioning commands.

Thrust:	9,870 lb
Propellant:	Aerozine 50/Nitrogen Tetroxide (hypergolic)
Mixture ratio:	1.6:1
Engine start capability:	20 times
Developed by Rocketdyne On loan from Smithsonian Institute

While Rocketdyne did develop a DPS engine as part of Grumman's competition for the engine, TRW's Space Technology Laboratories (STL) eventuall won the contract and built the engines actually used by the Lunar Modules. For additional information about the engine competition and development, see chapter 6 of Chariots for Apollo: A History of Manned Lunar Spacecraft.