A frequent problem with dive watches is that the luminous "pip" or triangle of the bezel is lost. This has caused a forum member to ask whether the luminous marker in the U-series bezels are glued in from the top, or whether they are secured against accidental loss, e.g. by being mounted from the other direction.
The answer from Sinn is that the U-series bezel marker is glued in from the top. To protect against loss it is lowered so that it will not protrude and glued in with a two-component glue which is also used in the making of surgical instruments (stomach probes, e.g.), giving it a substantial acidic resistance. Curing of the glue is done at high temperature.