A SIG RR can be represented as a single logical line in a zone data file [RFC1033] but there are some special considerations as described below. (It does not make sense to include a transaction or request authenticating SIG RR in a file as they are a transient authentication that covers data including an ephemeral transaction number and so must be calculated in real time.)
There is no particular problem with the signer, covered type, and times. The time fields appears in the form YYYYMMDDHHMMSS where YYYY is the year, the first MM is the month number (01-12), DD is the day of the month (01-31), HH is the hour in 24 hours notation (00-23), the second MM is the minute (00-59), and SS is the second (00-59).
The original TTL and algorithm fields appear as unsigned integers.
If the original TTL, which applies to the type signed, is the same as the TTL of the SIG RR itself, it may be omitted. The date field which follows it is larger than the maximum possible TTL so there is no ambiguity.
The "labels" field does not appear in the file representation as it can be calculated from the owner name.
The key footprint appears as an unsigned decimal number.
However, the signature itself can be very long. It is the last data field and is represented in base 64 (see Appendix) and may be divided up into any number of white space separated substrings, down to single base 64 digits, which are concatenated to obtain the full signature. These substrings can be split between lines using the standard parenthesis.