Its an numer of chests who is underground. Seen this both overland and in group dungeons.
The weird thing is that it looks like some items can clip trough terrain, objects they stand on top of, is one chest in banished cell who clips trough the rock it put on top of, you can still access a corner of it.
Its not only chests, one of the daily crafting writ delivery boxes at Rawl'kwa, think its the alchemy one sometimes fall trough the box its put on top of.
Why is my question. Is not these stuff static objects?