Officially, it's the 'Google Maps pin', that
"teardrop-shaped marker icon including a shadow"
which is part of its description found in the patent for the very thing you ask about. See Wikipedia on the Google Maps pin.
I note that the article says
The Google Maps pin has been called "a product of pure function that has evolved into a cultural phenomenon,"
which assuages my predilection for referring more to its function than its name. At least now I know what to call it, as before I was thinking just to say 'red bubble thingy' or 'red balloony thingy'.
Thus if pressed, I can call it a pin, map pin or pushpin:
a thumbtack with a spherical or cylindrical head of colored plastic, used to fasten papers to a bulletin board or to indicate positions on charts and maps
(definition found simply by googling for 'push pin define')
It's a more generic term than map pin (which I wouldn't use) and more pleasing than any such overlong term as location indicator, position locator, etc.
Although virtual tear dropped red balloony GPS/map indicator position-location marker thingy might work. ;)