|Par End Fedz EF-40 at W8BAE|
The 25 is the number of individual operating positions working simultaneously under the club call sign. The A designates a portable operation. Most stations I worked during the Field Day event ranged between 1 and 8 participants under the same call.
Thanks to Jeff, KE9V at ke9v.net for posting a link to this club's Field Day page. I thought the call seemed vaguely familiar and certainly the "25 A" rang a bell. I checked my log and sure enough that was the station I worked.
Follow the link: W3AO Field Day Page to see a truly amazing display of logistics and good old ham radio enthusiasm.