Day sporrans worn, at times, to the side is actually rather traditional. The ability to easily push a sporran aside is one of the features of a belt. Even with a kilt there are many occasions and activities where having the sporran pushed to the side is desirable.
I would not put valuables in it
Why? I would image that it would be safer than the typical handbag, rucksack or pants pocket (the rear is a particular favorite of pick-pockets). To cut the straps of a sporran to remove it in a crowd takes, I think, a bit more experience and daring than most common thieves would want to bother with. They might as well go the more direct route and just ask. Most of the pick pockets that cover European city centres are trained in handbags and pockets and looking for easy pickings (tourists, distracted mothers with their kids, shoppers with many bags, people who have drunk a bit too much etc.). Most work in teams and are part of organized gangs. Munich, like London, has quite a few CCTV cameras and large numbers of police (including many hidden from view and undercover)--- although not as many as you probably just saw (and the large number of VS and BKA as well as foreign bodyguards, secret services etc. you did not see) due to the Pow-Wow in Bayerischer Hof (yearly NATO "security conference" at the hotel and "anti-conference" on the streets).