Holy moly... I created a mess

wow...
OK here is some more details; we were having lunch without
anchor and the motor was off... We are in the middle of nowhere with no other boats around us... And the s/v was approaching heeled down most probably making a small runabout in a blind spot...
We are talking about a power boater guy who is the worst seaman I've ever seen, I needed to open the plastic package of the lifejackets to put them on on our way back, who not suprisingly doesn't carry an
anchor ball or any day signals...
All I had was my habit of keeping an eye around, common sense and my whistle...
This being the case, the sailboat could make a course change about 5 degrees and go around us, which they did. I was wondering how to signal someone to warn them about your location...
My fear is that when I'm on my sailboat underway slowly on power or stopped for lunck without dropping the
anchor, a powerboat that is in plowing mode may not be able to see me though I carry proper day signals... After all a 22 foot sailboat sits low on the water and when the sails are down it can be hard to notice if you are staring to sky...
Sound signals (in my boat that would be a
handheld horn or boat's horn) can be hard to hear if there is a mercruiser blowing beneath someone...
Visual signals are confusing for most powerboaters since they don't really know what it means...
VHF radio message may not work since their
radio is most probably off or they can't hear it due to engine anyways...
Oh f... it, I'll just move my boat away... There is no sense trying to warn a powerboater...
Common sense is safer than the colregs...
Sorry to create a turmoil ...