Hex head bolts don't usually come with a dome head, but there are dome nuts which, as you say are not stamped.
Some of the more decorative bolt heads, such as button heads, don't always have stamps, or sometimes they may have extra small discreet stamps
Those flanged head bolts would grind to a slightly domed face, or rather a very slight radius on the otherwise flat face of the head, once the stamps have been removed.
It does tend to make the hex part shallower, so greater care must be taken with the spanner/socket...This is no good if a highish torque is required. In which case another head style should be used.
Come to think of it button heads would look rather nice on the footrest hangers with those nice top hats.
http://www.westfieldfasteners.co.uk/..._SHBtn_M8.html
Don't use these for disc bolts though, they won't take the torque required.....As I found out..!!