A list of  Q-Signals

Q Signal Used As a Question Used As a Statement
QRG What is my frequency? Your frequency is ------
QRH Does my frequency vary? Your frequency varies
QRI How is the tone of my transmission? Your tone is 1 (good) 2 (variable) 3 (bad)
QRJ Are you receiving me badly? Are my signals weak? I cannot receive you. I receive you badly
QRK What is the readability of my signals? Your readability is (1) unreadable to (5) perfect
QRL* Is this frequency busy? This frequency is in use
QRM* Are you being interfered with? I am interfered with
QRN* Are you troubled by static? I am being troubled with static
QRO Must I increase power? I increase power
QRP* Can I decrease power? I decrease power
QRQ Shall I send faster? Send faster ------- WPM
QRS Shall I send slower? Send slower ------- WPM
QRT* Shall I stop sending? Stop sending
QRU Have you anything for me? I have nothing for you
QRV Are you ready? I am ready
QRX When will you call me again? I will call you again at ------
QRZ* Who is calling me? You are being called by ----
QSA What is the strength of my signals? Your strength is (1) barely perceptible - (5) very good
QSB* Are my signals fading? Your signals are fading
QSL* Can you acknowledge receipt? I acknowledge receipt
QSO** Can you communicate with -------? I can communicate with -------
QSP Will you relay to -------? I will relay to -------
QST   Calling all radio amateurs
QSV Shall I send a series of V's? Send a series of V's
QSX Will you listen to ------- on --------- kHz? I am listening to ------- on -----------
QSY* Shall I change frequency? Change frequency to ----------
QSZ Shall I send each word twice? Send each word twice
QTH* What is your location? My location is -----
QTR What is the time? The time is ---------

* the most commonly heard ones
** this has evolved, and now is commonly heard as "tnx fer the qso." meaning "Thanks for the chat."