Gemini shown. Non-Metallic channel letters can be used in wet or damp/dry locations. These letters can also be used in combination with other metallic channel letters.

Recommended bonding requirements are shown in the section below.

NOTE: Though 2 bonding options are shown here, only one is required for continuous bonding.

1. Standard Bonding with Rings, 
or
2. Custom Washer Rings for Bonding

Nonmetallic letters require continuous bonding between the connectors

NOTE: Rubber washer between back of letter & bonding plate

Grounding lug

All dead metal parts need to be grounded and a continuous ground plane must be maintained to insure the operation of the secondary circuit-ground fault transformers.

Grounding and Bonding: Metallic Grounding / Bonding: Nonmetallic Conduit Nonmetallic conduit when used in a high voltage circuit must be space 1-1/2” away from the grounding / bonding conductor to avoid the capacitance coupling and destruction of the nonmetallic conduit

This is generally a big problem for many UL2161 secondary-circuit ground fault protection transformers. Two things make a good ground: a grounding wire that is approved and is the proper size that can be traced all the way back to the breaker panel. Metallic conduit properly connected all the way back to the breaker panel.
NOTE: Gutters, metal building frame, flashing, sign base, painted surfaces, down spouts, etc. are not a good ground.  
You need to connect to a proper 3-wire (hot, neutral, ground) branch circuit. The ground must be firmly bonded to the transformer enclosure or box, raceway or sign body and to the transformers ground terminal (green nut) or wire is firmly bonded to this enclosure box or raceway and signbody. 
Please consult individual manufacturers web sites for the most up-todate, current servicing requirements.