I have two lucky coins on my electras gas tank on either side of the console and I used a cold weld product called kwick steel. It comes as a stick in a tube available under various name brands but theory all the same. Pinch off a small amount needed to do the job, nead in between thumb and forefinger until it turns a solid color, apply the product to the item your attaching, push the product in to position, and allow to set , sets strong and dries in 4 minutes, cures to full strength in 4 hours. Now the cool stuff is that it won't go anywhere unless you or yes someone else wants it to, but the really cool thing is that if you ever want to remove it , its very simple , simply pry it off and remove any remaining excess from the attached surface with acetone or acetone based nail polish remover and it all comes off with just a littlle minor elbo grease. I've attached many items decoratively speaking to my Harley's over the years and this stuff is the best, far and away easier than jb weld two tube mixture, plus easier to remove without damage, and for what you wanna do it is perfect.
Hope this helps I've used this a lot and it will go n tight and come off without ruining anything if your carefully during the removing process, it's especially great for attaching something to chrome or copper or nickel, or zinc plates. As with any adhesive product you always run some risk to the paint if you attach then remove from paint, but I have done that too with o damage.
http://www.horizonhobby.com/products...-epoxy-JBW8247
Peace I hoped this helped.