Not to be pedantic, but the first comma in your statement is incorrect; it should be removed. Try, instead:
Blockbuster, here, had a sale. The sign said, "DVDs on sale!"
Notice that "here" is being used as an adverb following a noun and is correctly separated by commas. Without the word "here," the sentence would be punctuated as:
Blockbuster had a sale. The sign said, "DVDs on sale!"
You may also separate "sale" and "the" by a semi-colon and change the "T" in "the" to lower case.
I should have spent a few extra seconds proofing my own post.
Now, with regard to the rogue apostrophe, I agree; it is incredibly annoying.
By the way, it's refreshing to know that in this world of electronic communications, where texting is destroying grammar and punctuation, there are still people out there who are even knowledgeable.
Cheers,
Bob