When you config(8) a kernel, it is assigned a version number, which will start with zero if this is the first time, or if you have delete the /usr/src/sys/arch/<ARCH>/compile/<KERNEL> directory structure. After that, the version number will increment each time.
There are several ways to see your kernel. For more complete information than uname(1), use either
$ sysctl kern.version
or
$ dmesg | head