Shostakovich uses his monogram in his symphony no.10.... DSCH. This equates to the notes D Eflat C and Bnatural. The H I understand as Bach used B natural to spell his name, but how does S turn in to Eflat?
In German (and some other Germanic languages, such as Dutch), the note "E flat" is written and pronounced as "Es", which has the exact same pronunciation as the letter "S".
There is some more information in the wikipedia article on the DSCH motif.
Note that Shostakovich used this motif in several of his works.
In several European languages the suffix "-es" means "flat" and "-is" means sharp, in note names.
Following the rule, "E flat" would therefore be named "Ees" but that is contracted to "Es" and pronounced the same as the letter "S." In some of the languages "A flat" is also contracted from "Aes" to "As".