Every coin has their own unique tracking number, and one of the types of log you can write for a trackable item on the geocaching.com website is a 'Discovered it' log. Some coins have their own icon on the site, and if you log a discovery, the icon of that coin is added to the list of trackable items you have seen.
Some people appreciate the coins for their beauty and design, some like the extra icon added to their list.
We carry our coins with us. When we meet fellow geocachers out in the field, we offer them to show them our coins so they can admire them and write down the numbers to log them as discovered.
But having four coins (average diameter: 43 mm) loose in the bag didn't help keeping them pristine and easily presentable. We had seen large binders with huge numbers of geocoins on the GME event, and I thought it would be nice to have a small album to carry the coins with us, to present to others.
Alas, the largest coin that has small albums available for it are coins with a diameter of less than 39mm. Geocoins simply didn't fit. After getting some additional info from die-hard coin-collectors, we decided to improvise a bit. We bought coin-holders and coin holder pages. Each page holds 9 coins, making it quite large.
I cut a page up into three strips, and cut one coin-space off each strip, to produce three strips of two coin-spaces. I used two of those to put our coin collection in, and I keep the strips together with a Paperclick.
The two strips with the paperclick. The coins are the GME coin (top left), the Reintje de Vos Memorial coin (top right), the gold 2007 Compass Rose (bottom left) and the gold ANWB Paddestoel coin (bottom right).
The assembled construction. If we acquire more coins, I can easily add another strip.
Extensible, easy and 'good enough' -- that's how I like it.