(netsh wlan show interfaces) -Match '^\s+Signal' -Replace '^\s+Signal\s+:\s+',''

Outputs the currently connected network's signal strength as a percentage.

You can also replace the two occurences of Signal with other titles you might want from the netsh command's output, such as SSID, BSSID (MAC address of the AP) or Radio type (eg. 802.11g).