That's what the tune or cw position is for.  A low SWR means their is 
little power being reflected down to your transmitter.  It does not 
garantee anything else, but you are likely to be radiating as well as 
that antenna system can.  Example, a dummy load should have a 
1/1  SWR, but naturally, it won't radiate either.  The proof is 
geting on the air and seeing what you can work.