My wife saw this yesterday on the side of a delivery truck.

Problem:
The sign maker used a verb where an adjective was required.

Explanation:
The delivery truck belonged to a retailer that sells home-theater systems.

The retailer uses the truck to deliver new home-theater systems for installation.

This gives us the solution. The word “Install” is incorrect on the sign because it is a verb. The sign maker should have used the word “Installation”, which is a noun that can be used as an adjective.

Unfortunately, at least in American English, it has become a common English blunder to use the verb “install” as if it were a noun, which it is not.

I believe that the misuse of “install” as a substitute for “installation” is consistent with my “Devolution toward Simpler” linguistic hypothesis. It is simpler to write the seven-letter, two-syllable word than to write the twelve-letter, four-syllable word.

Solution:
“Home Theater Installation Unit”