White spirits if it's oil based and not actually emulsion. Test an inconspicuous area first, but should be fine. The bodyshop that painted a panel for me use WD-40 which is essentially white spirit mixed with light oil. They use it mainly to remove tar spots.
Also, a clay bar is generally seen as a good first line of attack. If you use white spirit, lightly dampen a cloth with it and take it very easy.