What a screen reader actually does with a symbol
Screen readers (VoiceOver on Mac/iOS, TalkBack on Android, NVDA and JAWS on Windows) read text by looking up each character's name or associated word in their pronunciation dictionary and speaking that. A ★ isn't skipped or interpreted as decoration — it's typically announced as "star" or "black star," inserted audibly right where it appears visually. "★ New Feature" is heard as "star new feature," adding noise without adding the emphasis a sighted reader gets from the visual symbol.
Symbols that cause real problems
Repeated punctuation for emphasis ("Amazing!!!", "Wait..."). Some screen readers announce each repeated character individually — "exclamation mark exclamation mark exclamation mark" — turning intended emphasis into literal noise.
Emoji or pictographic symbols as the only signal of meaning. A ✓ (check mark) or ✗ (cross mark) used alone to mean "correct" or "incorrect" is announced by its Unicode name — "check mark" or "cross mark" — which only conveys the right idea if the listener already knows that convention. Pairing the symbol with actual text ("✓ Passed") removes the ambiguity for both sighted and non-sighted users.
Decorative symbols with no semantic purpose (dividers, bullet flourishes, box-drawing characters used as visual borders). A row of "═" characters used as a visual divider is read aloud as "box drawings double horizontal" repeated — pure noise in an audio context, better implemented as CSS styling than literal characters.
What works well instead
Semantic HTML and ARIA labels over decorative Unicode. A checkmark that means "task complete" is better implemented as an icon with aria-label="Complete" (or aria-hidden="true" if purely decorative) than as a bare ✓ character in the text content.
Currency, math, and other functionally necessary symbols are fine — they're meant to be heard. € is correctly announced as "euro sign," which is exactly the information a listener needs. The currency and math symbols on this site are functional information, not decoration.
If you do use a symbolic character for emphasis, test it. Behavior genuinely differs across VoiceOver, NVDA, JAWS, and TalkBack for edge cases like repeated punctuation — if accessibility compliance matters, testing with at least one real screen reader beats assuming based on general guidance, including this article's.
Why this belongs on a "how to type X" site
Every symbol on this site exists because someone wants to insert it into a document, and most of those documents will eventually be read by someone using assistive technology. Knowing how to type a character is only half the picture — knowing what it does when it's heard rather than seen is the other half.