"What does the $ (dollar) sign in front of a stock ticker/symbol mean"
Aside from the Twitter significance, it's also an excellent indicator that the stock in question is the subject of a paid promotion on the Internet.
Like OGINVU says, those stocks are worth staying well away from.
"It is difficult to get a man to understand something, when his salary depends upon his not understanding it."
Upton Sinclair
"Nobody ever went broke underestimating the intelligence of the American public."
H. L. Mencken