It is a RAF Mark 11 as you already said. Some collectors like the "hooked 7" dial but, IMHO, it does not make the Mark 11 more collectible. The Mark 11 was an important tool watch for astronavigation and the "hooked 7" is an irrelevant detail adding nothing to its qualities.
It is highly unlikely your Mark 11 had been in use by the BOAC. We know very little about the BOAC Mark 11s but, the few extant ones we have a high degree of certainty were used by BOAC, do not have the pheon on the dial. The pheon was used only by the Royal Air Force and the Royal Fleet Arm, and for a while by the Air Forces of some Commonwealth members. A dial with a pheon on a BOAC Mark 11 is more likely to be a recent addition, than be original to the watch.
If you search BOAC in this forum you will find several discussion on the matter.
The case back is an original military Mark 11, without case number, and does not make it more likely to have been used by BOAC.
As to the absence of engravings, the simplest, and most likely explanation, is that, whoever owned after decommission, erased them for whatever (regrettable) reason.
