Specific empty children classes

Is having empty children classes, just to specify, a bad practice?

Lets suppose I've a generic Product class. There are electrical, electronic and mechanical products. I need to represent all them and must be able to differ each one in some operations. I've two options:

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  add a member named "type" in Product class to specify whether it's a electrical, electronic or mechanical product.

  
  


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  create children classes of Product, one for each kind of product: ElectricalProduct, ElectronicProduct and MechanicalProduct. As these classes don't differ from each other in methods or members - already defined in parent class - they would be all empty.

  
  

I consider second option a better approach, but is it the right way? I've never seen such thing on any application or library.

What do you thing? Any suggestion?