Rather than trying to guess what device numbers mean what (which will vary between systems and even versions of the "same" system, especially with modern Linux kernels where /dev is assumed to be a RAM filesystem populated at boot), the better way to determine what is on a mountpoint is to examine the output returned by qx/mount/. This will allow you to easily determine if a mountpoint is a RAM filesystem, but there is no one reliable way to determine if a physical block device is actually a RAM disk, especially a hardware device, which may even be relatively non-volatile with battery-backed storage or an SSD that can retain data with no power at all.

I suspect that our questioner is concerned with ensuring that a RAM filesystem has been mounted before some daemon begins its work. In this case, there is a bit of an XY problem here: the real concern is that a filesystem has been mounted on the designated directory, since other configuration ensures that that filesystem will be the intended RAM filesystem.