I don't recall that sort of symbol in my electronics background. The circle itself is a common part of many electronic symbols. For instance a "V" inside the circle indicates voltmeter, an "A" an ammeter, "W" a wattmeter (also a "P"). The circle is also part of the symbol for a lamp, an outlet, a plug, a signal generator and a host of others. Is there any other information you can give with this symbol, are you sure it is a "7" and a "1"? Good Luck.
