I invest in silver usually by buying 1 once coins from mints of good reputation like this one.
https://www.muenzeoesterreich.at/eng/vienna-philharmonic/silver
There is no better way than buying physical silver!
But there are numerous other possibilities to invest in silver, even here on Steem:
https://steempeak.com/hive-167922/@thesilverpenny/the-silver-penny-project-silver-discounted-0-777-slvp-blowout
And last not least the Steemsilverrounds:
https://steempeak.com/steemit/@ssg-community/2019-steem-silver-round-now-on-sale
But for spinvest, I would not recommend - there is no functional market for those coins. Could be a good investment, but the risk is high.