When you use flint and steel on cobblestone and mossy cobblestone walls in the centre of a long wall (like 3 across so there is no pillar in the middle) on the top of the wall, a quick image of a pillar shows on the wall. i know its only small but i thought i should tell you.

i couldn't get a screenshot for you but i recorded it for you

http://youtu.be/g09ZC3V-q0c