The following license plate number is italicized in print: GMT 588. Would each segment be italicized separately i.e., use two italic word indicators? I'd prefer to use a numeric space between the "T" and the "5" since the two segments seem like they should be kept together as a single unit and then use just one italic word indicator at the beginning. But I'm not sure that Rules of UEB 6.6 can be applied here since there are letters and numbers.
Glad you asked! Each symbols-sequence needs to be italicized separately. The numeric space indicator is only used for numeric segments of a single number. It isn't meant to keep symbols-sequences together in general. It would not be appropriate here because the letters GMT do not represent numbers.