Forums have an icon by Canik for this for some iso (amplio/amplio2?) tileset: http://forum.freeciv.org/f/viewtopic.php?f=12&t=91999#p104138
amplio2 & amplio part -> #43003
Keeping this ticket open as a meta ticket for tileset specific ones.
hexemplio -> #43151
#42920 makes client to show a "cursor" sprite in a tile where user is currently placing infra to. That's tag "user.infratile" from the tilesets. As a temporary solution, all tilesets are reusing "user.attention" for this, but it would be good to add distinct graphics for it.