If you want to avoid an over the top questioning by the Airport security and subsequent anal probe it is probably best you do not own a Casio  F-91W. The digital watch is common as muck and is as cheap as chips, but apparently it is being seen as evidence of  having bomb-making training.

Guantánamo Bay interrogators are convinced that owning the watch is a sign of al-Qaida training and this has prevented many prisoners stationed at the US prison from going home. A report has revealed that the Casio was known to be given to the students at al-Qaida bomb-making training courses in Afghanistan at which the students received instruction in the preparation of timing devices using the watch.

More than a third of the JTF-GTMO detainees that were captured with these models of watches have known connections to explosives either having attended explosives training, having association with a facility where IEDs were made or where explosives training was given, or having association with a person identified as an explosives expert, the report said.

More than 50 detainee reports refer to the Casio timepieces. The records of 32 detainees refer to the black Casio F-91W, while a further 20 make reference to the silver version, the A-159W. So either way if you want calm flight without being hassled by security it is probably better to leave your watch at home.