“Shurp… Shlurp….Slurshpee?”

OK I pull up to the 7-Eleven by my house and notice this marketing sign prominently displayed in the window. The sign was made to LOOK LIKE a homemade "lost and found" type sign that said "SLURPEE" across the top. Near the bottom it said "I lost my Slurpee 866-696-7829 Reward If Found." That is all it said. There was no expanations. I was not interested enough to call the number, but decided I would ask the cashier. So, when I asked, he replied "Shhhurrrpeee?" He seemed confused at best. I tried one more time only this time I enhanced the question with a visual aid. I pointed out the sign in the window. I figured that might help. Well it did not he replied "Shurp...Shlurp...Slurshpee?" He then called the other cashier over and said something that sounded like a string of vowel sounds being uttered in the oscillating tone of a British siren and ending in Shhhruppee. The other cashier replied "Shhwuppy?" He looked a me then said "Shwuppy? you want Shwuppy? - I get you Shwuppy. What flaywer?" Here I am still in mid gesture pointing to the sign in the window. I was convinced that if I keep pointing to it that soon my question would be understood. How can 7-Eleven have a promotion and not tell their employees anything about it?