Could you post again and describe the symbol, or give an address where we can view an image? Without knowing what this looks like it's impossible to guess its significance. There are many reasons why a phone could lose signal: a problem with the phone (hardware or software), the SIM or the network could all do this. If you have another phone you could eliminate some of these, e.g. by swapping the SIM to the other phone (if you have the same problem with a different handset then it's the SIM or the network).
