Best marker for writing signs with wide, even strokes?

Hi,
I'm looking for a marker (like the ones used on whiteboards) which is good
for writing with wide, even strokes.
The typical wedge-tipped markers aren't actually all that effective, because
if one holds the marker stationary while writing the letters, the strokes
have an uneven width, and I have to go over the letters again to even it
out.

So, I think I'm looking for a marker with a wide, round tip, which is FLAT
on the end. This marker would be held perfectly upright while writing, and
the strokes should end up being nice and even on the very first pass.

Does a marker like this exist?

Thanks,
Greg.