OSTree revisions are identified by a commit hash, just like in Git. You can check the revision running on a device with ostree admin status.

The output should be something like this:

$ ostree admin status

* agl fcac1276197670dc98bd082d3edd8e2dd8b349cd0ff7b4529ce103e45882514a.0
    origin refspec: fcac1276197670dc98bd082d3edd8e2dd8b349cd0ff7b4529ce103e45882514a
  agl c399da4079f5de110bf8c2c379656ee0c08406daa479407074492ec226462639.0
    origin refspec: c399da4079f5de110bf8c2c379656ee0c08406daa479407074492ec226462639

The commit with the star next to it is the currently deployed image.