As K1KP (and others) stated, sending Vs or a series of Vs is only a test signal and not an inquiry as to whether a frequency is in use. QRL, albeit an appropriate means of determining if a frequency is busy, in my opinion, is not as efficient or courteous as the prosign used from the early days into the 1960s: sending the letters I E. Didit dit is succinct and gets one's intent across without oozing-out a long, drawn-out Q signal. After sending a quickie "Didit dit", a station in QSO on the frequency needed only to send the letter "C" meaning "yes." Done!
I feel it is even less courteous to send "QRL" followed by unnecessary question marks. A protracted "QRL QRL ? ?" consumes seconds which often obliterates a great deal of an unheard station's sending that someone is trying to copy.
DE WA9VLK