The plaque lists the names of locals who volunteered as part of the International Brigade during the Spanish Civil War between 1936 and 1939, against Franco.

The plaque was re-dedicated in Middlebrough Town Hall in 2009 after being found in 1983 in a junk shop in Acton, West London. Some of their stories are in this BBC article

Thanks to David Walsh and John Buchan for bringing this to my attention and providing the photo.