To avoid '?' and '' characters in reporting, collect only single byte characters in your implementation.
Multi-byte characters collected in tag data sent to a single-byte Digital Analytics Client ID appear in reporting as '?' and '' characters. This commonly occurs when multi-byte Trademark (tm) or Registration symbols are included in otherwise single-byte data. Other symbols such as '-' (dash) have multi-byte and single-byte versions. Where possible, collect the single byte version of these characters in your single-byte Client ID implementation. Contact your Digital Analytics Account Team or Sales Representative to discuss changes in data storage settings (single-byte vs. multi-byte).