This is by far our most asked question. So how do you know what unit is in your e30? Well, here are a couple of ways you can tell.
The first way: Stamping on face of gauge cluster
Your e30 3 series or m3 will have the either "vdo" or "motometer" stamped in the gauge cluster between the RPM and speedometer. Note: This is not always correct (we can say it is about 70% of the time). Some Vdo units ended up coming with moto gears and vice versa. This can only give you an idea.
The second way: taking the cluster out
This is the most accurate way. As you take your cluster out of your car (best to remove the steering wheel (7/8 or a 21mm), but be sure you're careful with the clusters V-tabs when removing!), you will notice stickers on the back of the cluster either saying "moto" or "vdo". As you open up the cluster (instructions can be found here: Taking your cluster apart) you can make absolutely sure by looking at the actual gears. Pictures below:
Note: Moto stamp on back side example:
(sticker above is a good way to tell!)
Vdo gears pictured below:
Moto gears pictured below: