They probably never even read what was on it, or if they did knew the background to it.
That's either naivety on your part or staunch (and blind) defence of "fellow servicemen".
1. They know what's on it. You and I wouldn't stand behind a banner or a scarf with smug grins on our faces without knowing what was on it. Football scarves are double sided by the way, they say the same on the reverse.
2. If a soldier doesn't know the background and gravitas of the name "Ulster" as it relates to the British military he's not been brought up properly in his basic and trade training. That reflects very badly on the forces whichever way you look at it.