-s --s19

Request to write the output file in Motorola S-Record format. This is only allowed for target ROM (the default) or target BIN.

This format supports a header and zasm uses it to store the source file name and assembly date. Since it is encoded as hex data, it is not directly readable in the #insert: Examples:
#assert: Example:
incbin: Examples:
#assert: Example:example below:

S00F00007320323031352D30312D313178
S12C00003E00ED79ED79ED793E40ED793EDAED793E37ED79ED780F30FB3A1027D370ED780F0F30FADB7032102772
S5030001FB
S9030000FC