I think that Sigmund is trying to use the s character as the delimeter in a substitution. Replacing this with / changes the code from

perl -le 's ssSss.s sSsSiss.s s$sSss.ss .$s\107ss.print'
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to

perl -le 's //S/s.s /S/Sis/.s /$/S/s.s/ .$/\107/s.print'
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This prints

SisS
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Sigmund, is this correct?

UPDATE:
I have just read this node: Beware the S ! where Sigmund explains his signature, so it would appear that there was just a typo in the original post.

The correct version,

perl -le 's ssSss.s sSsSiss.s s$sSss.s s.$s\107ss.print'
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works fine and prints

SiG
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Basically the 16th s should have been after the space, not before it.

JJ