I've never used a dial indicator for this. Usually I can use a long skinny screwdriver.
There are special tools for this though. This is one I found with a Google search using "TDC Tool". This one happens to be for a motorcycle engine, but that shouldn't matter as long as you have the correct spark plug thread. It is about half way down the page on the right hand side.
http://www.aperaceparts.com/tools.html