If you're interested in melting it to make something out it, it's reasonably easy to make little ingots using borax flux to remove impurities.
There are loads of resources out there for people interested in making silver jewellery that cover melting and casting metal. For instance, I find this jeweller's videos on youtube really informative and easy to follow.
As Stefffana said, it's best to keep hallmarked scrap whole if there's a chance you'll be selling it on. Mystery ingots are too much of a risk for most people. Even if you manage to sell them you won't get as much as you'd have got for the scrap. If I were doing a one off, I'd try to find a friendly jeweller (or silver pouring forum member) and agree a price to get my item included in a batch that they are sending in (if the assay offices allow this)
Definitely look into hallmarking if you want to make anything to sell on. I think assay offices might let members of the public submit pieces for testing, but the price is much much higher than what they charge their members. Membership's not too pricey if you're actually making this into a business, and once you are submitting items in batches the cost per item is low.