I was recently pulled over whilst riding my pushbike. They searched me and did a numbers checks on the bike which came back as not stolen, which I already knew as they had previously done a check 5 weeks earlier. This time, they took it and said they were sending it to forensics for further testing. I know the bike is legit, but I don't have the sales receipt to prove as it was bought for me as a gift for my birthday. I asked the person who gave me the gift if they still have it, but they told me they had purchased it at a trash and treasure markets. My question is, how can I prove ownership without the receipt under Property Law?