If something is doubtful it is uncertain, and one needs to know more about it: The weather looks doubtful (it may rain, but it may not). If a thing is dubious it raises or causes doubt: He gave a dubious reply when I asked him about it; Christine had the rather dubious privilege of staying behind to keep an eye on things.
The emblem reflects the Vatican's importance as the headquarters of the Roman Catholic Church. The colours of the flag are based on the gold and silver of the papal keys. Effective date: 8 June 1929.