⃝

Symbol

 * 1)  marks an enclosed symbol as being indistinguishable or unidentifiable.
 * 1)  marks an enclosed symbol as being indistinguishable or unidentifiable.

Usage notes
A circle without an enclosed letter, $⟨◯⟩$, is completely unidentifiable. If some feature of the sound can be identified, a wildcard or best guess may be enclosed. For example, σ⃝ is an unidentifiable syllable, C⃝ an unidentifiable consonant, k⃝ perhaps [k], etc.