These objects have one or more tagged polygons, which have been internally given a tag value to distinguish them from other surfaces.
An internal tag value of 100 works with the sign command to display text on the tagged surfaces while polygons which have been given a tag value of 200 will work with the picture command which allows you to place a specified JPEG image from the web onto the specially tagged surfaces.
Any tag value can be used with the animate and texture commands which each support a special tag parameter.
There are many objects in this list with tag values such as 300, 400, or 500, on one or more of their surfaces.
Check the list of sign objects for additional tagged objects with a tag value of 100, and the list of picture objects for additional tagged objects with a tag value of 200.