This is the WTS rule, policy, law on it on a related topic:
km 9/74 p. 8 Question Box
Is it fitting to display the Hebrew or English letters of the Tetragrammaton on automobiles, jewelry and other items?
This is a matter that should rightly be left for each Witness to decide, based on the dictates of his own conscience.
Nevertheless, circumstances vary, and what may be appropriate in one locality may not be fitting in another area. For example, where there is considerable prejudice against Jews, displaying the Tetragrammaton in Hebrew letters could give rise to needless problems due to mistaken identity. And some Jews themselves find the public display the Tetragrammaton objectionable. Also, in some areas there are other reasons why such a practice might be viewed as strange and so create misunderstandings.
On the other hand, some have found that displaying the Tetragrammaton either in English or Hebrew letters has aroused curiosity and given openings for informal witnessing. Then, too, it has served as a means of identifying other Witnesses when traveling.
If a person should decide to display the Tetragrammaton on his car, he should also appreciate the responsibility of not misrepresenting it by disregard for Caesar?s laws or by careless and inconsiderate driving. (hahaha)
As Jehovah?s servants we are responsible to uphold the dignity of his name. This is done primarily by preaching and by setting a good example in Christian living. Should the public display of the Tetragrammaton detract from that, it would obviously not be fitting. Furthermore, we do not want to give others the impression that the Tetragrammaton is the symbol of Jehovah?s witnesses as a whole. We have no organizational symbol to identify ourselves but show that we are Jehovah?s Christian witnesses by living in harmony with God?s will.?John 13:35.