Criminal Sentence 245: Three for One

I had to get new tires yesterday and, being myself, I couldn't help but copy down the text of a large sign in the showroom:

"Underinflated Tires can decrease fuel mileage by 10%, that can add up to hundreds of dollars a year"

I had to sit next to this sign for 45 minutes! What horror! What torture! (OK, I'm exaggerating just slightly.)

Three errors:

1) No need to capitalize "Tires" unless you're talking about a proper name. Is some naughty person named Underinflated Tires going around and decreasing fuel mileage?
2) A comma between two sentences is called a comma splice. Comma splices are no-nos. There's a new invention the sign writer hasn't heard about: a period. A period ends a sentence.
3) What, a period is missing at the end of this sentence? Yikes!