In my hometown there are two septic service companies. The slogan for one is disgusting: "We Deal In Used Food."
The other one is kind of clever: "A Royal Flush Beats a Full House."
I don’t know if it’s still there, but Mesa, Arizona used to have a landscaping/sprinkler installation company whose slogan was:
Let Mesa Sprinkler put a bubbler in your bush.
There’s an Auto Parts store near me that has this cyclical slogan.
“If it’s in stock, we’ve got it!”
How dumb.
I’ve seen a septic service company whose motto was, “It smells like money to me.”
Anyone remember when cigs were advertised heavily on TV? And the millimeter war started? And someone (I think Winston) had the slogan:
“It’s not how long you make it, it’s how you make it long!”
That’s worked for me ever since I was introduced to the exotic pleasures of the flesh 
Here in Los Angeles County, on the 210 freeway in Irwindale there’s a billboard for some pop 40 radio station advertising its mandatory obnoxious morning DJs. Their slogan?
“Less Painful Than Waxing”
Mad Magazine once advanced the theory that LSMFT meant “Lucky Strike makes fatal tumors.”
-Myron
Frank Perdue’s slogan on Mexican billboards:
“It takes a hard man to arouse a chicken.”
I liked the one used for an all-too-brief time by the Juan Valdez/Colombian Coffee folks: Grab Life by the Beans.
Apparently, A&P Supermarkets used in the 1970s, “We’re always working for your WHEEE-OH!” Apparently, their prices were so low, they’d make you shout “WHEEE-OH!” Are those ad writers on drugs or what?
There’s a muffler shop in Pine Bluff who’s slogan is, No Muff Too Tuff.