Background Reading: 6-E: Legal Certification 

If you plan to get a permit which requires an inspector to sign off on it, they’ll need to see a plaque on the hot tub showing that it has the ETL mark as proof of product compliance to North American safety standards (Canadian and USA).   See 

Tips:

-Look for the plaque showing the certification stamp.  It may be made of metal, plastic, tin foil or just a vinyl sticker.
-This plaque often also shows the volt/amperage rating, serial number and manufacturing date.
-It’s usually fastened somewhere on the cabinet, but sometimes can be found inside the equipment bay on the wall or on the back of the access panel 
-If you or the seller cannot find the plaque, either walk away, or ask for a discount based on the risk you’d be taking.