Information is scarce on the bridge but a local website had the following info :
. One of the most famous sights on the canal is the so called Laughin' and Greetin' Bridge, the Glen Bridge near the eastern entrance to the tunnel. Here the bridge builder has decorated the keystone of the arch on either side with a laughing face (facing Edinburgh) and a crying face (facing Falkirk). The reason? One theory without much evidence is that the section between the Glen Bridge and Falkirk involved the construction of the eleven locks and the cutting of the tunnel, a tougher project than the section to the east of the bridge!
Another possible explanation has been postulated that the contractor undertaking the easy section to the E became rich, whereas the tunnel and locks to the W caused that contractor to go bankrupt.
Gps signal is a bit ropey here but with the clue it can only really be in one of two places.
Please carefully replace as found.