The Bid and Ask Prices are available from the brokers on a real-time basis through an API. The display of this information on a graph is better information than the volume alone. Large Bid and Asks spreads shows that there are limited buy and sell limit orders though the Market Makers that the Broker has communication(s) with. There are times where the volume is high but the shares are traded through ECNs and not through Market Makers. Tradeking orders are sent to the BATS Market Maker. IB shares are handled by their "SMART" system and IB is involved with many Market Makers beyond BATS.
IB also has information about stock trading being halted and not being shortable by SEC restrictions along with the number of shares the Broker has available to short. Displaying these items as a note would deduce the time wasted by trying to submit a short order that can't be filled. A temporary halted note could explain while the volume is zero.