The red "F" is a Fast Market Indicator. A "Fast Market" is one in which the speed with which a security's shares are traded is so rapid that the most recent quote may be outdated before it can be reported. This is a temporary occurrence and usually lasts for only a brief period of time.
In addition, the following conditions will appear as text next to a symbol in any eSignal Pro window that receives Quote information whenever these conditions occur:
red H means that trading has halted on this issue
A red R means that there are special restrictions governing trades on this issue
A red X means that a symbol has gone X-Div