A circled number ①, ②, ③, etc. represents the 1st, 2nd, 3rd, etc. item.
2013, Emily Laurence Baker, Slow New Forest: Local, characterful guides to Britain's special places (in English), Bradt Travel Guides, →ISBN, page 109:
④ New Forest Wildlife Park Deerleap Lane, Ashurst SO41 4UH Ⓣ 023 […] Ⓦ www.newforestwildlifepark.co.uk
A circled letter Ⓐ, Ⓑ, Ⓒ, etc. represents the Ath, Bth, Cth, etc. item.
2004, Faye Berryman, Philip O'Carroll, Fitzroy Word Skills 3 Answer Book (Stories 21-30) (in English), Lai Lai Book Company, →ISBN, page 75:
Fill each gap below. Use the word from the story. Ⓐ It seemed that she just didn't like her toys. Ⓑ But her mum answered, “I don't have time...” Ⓒ I really like talking.
(extIPA): A circle without an enclosed letter, ⟨◯⟩, means a completely unidentifiable sound. 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 is an unidentifiable consonant, k⃝ is perhaps [k], etc. This is effectively a copyediting mark and, like other such marks, is not intentionally supported by Unicode.