In this case, I think you're referring to "Star Grading Service", a company that evaluates coins. (There is also an "SGS" that's industrial.) When a coin is "certified", it is authenticated by SGS. Most coin investors won't purchase any coin of value without it being verified of its authenticity. The "1d" simply means One Dollar. A penny would be "1c" for one cent, a dime is "10c", etc. Hope this helps!