Here is a list of other substances that can remove stickers:
< cellPadding=10> <> < vAlign=top>WD-40lighter fluidlacquer thinneryour fingernailwarm soapy waterrubbing with your fingersdenatured alcoholturpentinemineral oilfurniture oilpaint thinneracetone < vAlign=top>
finger nail polish remover lift it off with (scotch?) tape a razor blade scraperheating with a hair dryerheating with a heat gun on low3M adhesive removerGoo GoneGoof Offbaby oilvegetable oilCrisco
With some of these you can get more effect on stubborn stuff by letting it soak for a while after wetting it. Others must be wiped off fairly quickly to prevent marring the finish or evaporating.
If there's any doubt whether it will harm the surface, test on an inconspicuous area first.
If you plan to paint afterward don't choose an oily one like WD-40 or Crisco
I worked as a janitor for about 3 years and the best method to clean mirrors and windows without streaking was to use paper towels, soap and water, and clean from left to right from top to bottom.