Foreign vehicles do not need Spanish Low Emission Zone Stickers. 

Affects Madrid, Barcelona, Seville.

While the Spanish 'Distintivo Ambienta' Low Emission Zone Stickers are mandatory for Spanish vehicles, they are only voluntary for foreign vehicles

The Stickers can be purchased from post offices or selected vehicle workshops, but cannot be posted out of Spain. Therefore the Sticker requirement does not count for foreign vehicles. For more information go to Madrid.