I thought that they might be insulators to keep different phase power lines from clashing and shorting out in high winds. I used to think that they were warnings to low flying aircraft, but some of them are so low that they would have to be real barn stormers, rather I think those might warn house-movers. My dad even joked that they were helium floats that helped hold up long runs of power lines. Lastly, I just kind of guessed that they might be a physical impediment to rats running from building to building.
I couldn't find one of my old photos of them quickly so I drew this picture in paint:
Okay since I can't attach a picture or comment, here if you GOTO 29.802881445882463, -95.40362637042956 coordinates in google street views, and look up at the power lines above the stoplight, you'll see the two balls in question, also about two blocks away you'll see a hospital that has a very active life-flight helicopter...DUH! I've always been picturing biplane cropdusters! Not airport, helipad. Good link skeptik.
Okay, so here's the real kicker anonymous, that instead of being near an airfield, out in the open anywhere, or near a busy heliport, they were on a powerline strung between two buildings in a residential street about thirty-five feet above the yellow stripe. To become relevant you'd have to fly down 19th street between the Venus hair salon and some antique shops. Look out for that low hanging stoplight!
