Hello,
"CM" probably refers to "central meridian". The central meridian of UTM 30N is 3°W, so it seems a good bet that WGS 84 UTM 30N is the correct coordinate system. You should be able to verify this by doing the following:
- Use "Define Projection" to assign WGS 84 UTM 30N to a copy of your data.
- Load the result in a map and check that it agrees with either a base map or with data for which you know the correct coordinate system.
-Charles