Sentence:  He knew it would be risky parking on a <WSD>double yellow line</WSD>, or even a single yellow line, at this hour, but in a side street off the back of Kensington Church Street he found areas demarcated on the roadway with white lines. 
Meaning of the word marked with <WSD> tags:  A pair of yellow lines painted at the side of a road to show that parking is not permitted at any time.