Which Q signal indicates that you are receiving interference from other stations?

The Q signal 'QRM' stands for interference from other stations or man-made interference. A helpful mnemonic is to remember the 'M' in QRM stands for 'Man-made' interference, such as other operators transmitting over the frequency you are using. Other Q signals in the options have entirely different meanings that are frequently tested. 'QRN' refers to natural noise like atmospheric static or lightning, where 'N' can stand for 'Nature'. 'QTH' refers to your location, and 'QSB' indicates signal fading.