Understand that the cheapest 'magical loot' is worth thousands of nuyen; serious stuff is worth tens and hundreds of thousands, and if they're picking up 'anything not nailed down' and you state that there's a bunch of things, they can easily walk out of there with a million or more.
This means 'the people they steal it from are definitely going to come looking.' This is the sort of thing that's the start of a whole series of issues for the PCs, even if they play their cards right.
That said, you are essentially looking at 'stuff that fits what the book says'. This isn't D&D, where you can (normally) have a little gizmo that does something interesting all on its own; a focus in SR requires a magically-active individual kicking it, or a summoned-and-commanded spirit at the very least. Things that don't fit into that general viewpoint are either dangerous ('Bottled Demon'), powerful ('Bottled Demon', the essence focus possessed by Martin de Vries), or peculiar (the 'attention focus' used by the Tir na nOg assassin Teachdaire) - and often all three. Otherwise, unusual magical items are rare and made for a specific, usually target- or time-sensitive purpose: 'Bind the House On The Hill Demon', or 'Gather Power At The Utter Dark of the Moon on 23 September' (which happens once every seven years or whatever, and is keyed to the two hours on either side of the exact time the moon is at its darkest, which in turn relies on a specific longitude on the planet which changes each year). These things are usually very expensive, insanely tedious and unique, and will typically work very rarely, but since they're made for a specific reason, the owner will definitely come after it.
Something 'unusual but safe' is likely to fit under the 'normal focus, unusual shape' category: a power focus designed as a pair of handcuffs, for example. But remember, you are still looking at tens and hundreds of thousands of nuyen just for that pair of 'cuffs, depending on the power of the focus. So just remember - stealing one or two small thing (in this case) might be doable, but stealing a lot ... well, it can really bump your game to a whole new power level. Be forewarned.
