[TUHS] What's In a Prompt String?

[segaloco via TUHS]

UNIX has had several ubiquitous PS1s: @, %, $ and then a PS2 of >, with these values also being configurable.  I've seen in various BTL media folks using a . (period) or occasionally a $ but with no space between the prompt and the command.  I've always assumed the former was influenced by DEC and the latter by IBSYS control cards (e.x. $JOB, $EXECUTE, etc. pre-JCL stuff).

Is there any history on the rationale for default PS1 selections between various shells?  Worth noting that % seems to be the most commonly implemented but $ is what more people are familiar with due to the adoption of the Bourne shell by V7 and subsequently various standards.  I mention the % as more common as it seems to be default in a greater number of shells despite Bourne family generally having more uptake (afaik).

Did these choices of symbols have any particular significance?  I can't recall where I read it but I heard suggested the original UNIX shell used '@' as a prompt as it looks like a snail shell.  Can't verify this, nor do any stories of the other symbols come to mind.  I've found the ubiquity of PS2 '>' in graphical icons for terminal emulators odd.  That's not a super common prompt to see on UNIX compared with the others, I find it strange that is often the prompt character chosen for icons, implying users are often sitting at a PS2 prompt?

- Matt G.