Hi Ahmad,
Those special characters are not allowed as chain IDs. It is not just a Chimera(X) requirement, but part of the PDB/mmCIF format description, for example described in:

<https://www.wwpdb.org/deposition/preparing-pdbx-mmcif-files>

"Each polymer chain must have a unique chain ID. Permissible characters are uppercase letters A-Z, lowercase letters a-z, and numbers 0-9. PDB format allows only single-character chain IDs, while PDBx/mmCIF can accommodate chain IDs of up to four characters.”

I hope this helps,
Elaine
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Elaine C. Meng, Ph.D.
UCSF Chimera(X) team
Department of Pharmaceutical Chemistry
University of California, San Francisco

> On Jan 8, 2020, at 8:11 AM, Ahmad Khalifa <underoath006@gmail.com> wrote:
>
> I can do "show #2/m cartoons" for a chain with ID m, but for a chain with ID % or $, I get:
>
> show #2/% cartoons
> Expected a collection of one of 'atoms', 'bonds', 'cartoons', 'models', 'pbonds', 'pseudobonds', 'ribbons', or 'surfaces' or a keyword