In some cases, if you enter a signature with field items, color lines, bold options, etc. or a long message, the signature is not fully displayed in the OWA.
Exchange server limits the signature size at 16 Kb. If the signature exceeds this limit, it is truncated.
Please refer to this link for more details.
Please try to adjust the signature in the limit of 16 Kb (as 1 character is approximately 1 byte, you can have 16000 characters). Also, try NOT to use fonts which are non-Microsoft fonts because they take a large amount of bytes.
Applies to: All versions of MC
Reference: TFS #18345
Knowledge base ID: 0139
Last updated: Feb 24, 2016