I suspect that you might be referring to the SHC’s (“Seller Help Content”) FBA Product Title Requirements (link, old style, will redirect to Help Hub Revision v.), which for many years has included this:
"…
2. Titles must not contain characters for decoration, such as ~ ! * $ ? _ ~ { } # < > | * ; ^ ¬ ¦
…"
To be fair, the same or similar prohibition has for many years existed in various other SHC & CHC (“Customer-facing Help Content”) pages, various BTGs (“Browse Tree Guides”) & Category-specific Style Guides - sometimes, but not invariably, with that same text as reproduced above, or in a few cases one or another variation of the specified Special Characters List - but it must be admitted that the Editorial Team has been engaged in paring down what were once detailed specifications ever since the 2018 Help Consolidation Initiative first brooked dawn - a trend which has only accelerated with the 2020 Help Hub Revision Initiative; a prominent example of this phenomenon is the evolution of the long-time ‘parent-index’ page Product Title Conventions (link, old style), which in its current version includes no Special Character List at all - merely a relatively-vague implication that such does exist, for most-any machine language one chooses to use, apparently being considered sufficient.
I’ve never been a Handmade Artisan, but I long paid attention - in the Jive & Discourse iterations of the OSFE, outside of the Closed Handmade fora - to posts by those who are; you, Image, Puppy Love, Aerides, And Then Some, Baer, Joe, Celtic, Ana, Wode, Chimanimani, Elm Street, Otis, Dreamscape, Roots, Meredith, Moonstone, Wade, MMacBabies, and many another of y’all’s compatriots have taught me much over the years by having done so - and as a result I became aware that there were/are some fairly wide variances in the Handmade & Custom Program’s requirements and/or allowances.
Still, I was not until now aware that certain Special Characters were supported for Handmade PDP (“Product Detail Page”) Titles.