Quote Originally Posted by oldboy
'I saw (that) he wrote 'I was here' with a felt pen on a wall'?
Perfect.

"I saw that he wrote..." and "I saw that he had written..." are very similar in meaning. If I'm not mistaken:

"I saw that he wrote" = Simple Past
"I saw that he had written" = Past Perfect

Maybe this will help: http://www.englishpage.com/verbpage/verbtenseintro.html, or someone else can explain the difference better than I can?