The International Phonetic Alphabet (IPA) uses a period or full stop (.) to mark syllable divisions. For example, the word "syllable" would be transcribed in IPA as /ˈsɪ.lə.bəl/.
References:
Handbook of the International Phonetic Association: A Guide to the Use of the International Phonetic Alphabet, Cambridge University Press, 1999, page 30. The Handbook explicitly states that syllable breaks are marked with a period: "Syllable breaks... may be marked with a period."
The official website of the International Phonetic Association has a chart of the IPA with descriptions of each symbol. It says that "Minor (foot) group" (which is essentially a syllable group) is marked with a period. (https://www.internationalphoneticalphabet.org/ipa-charts/ipa-symbols-with-unicode-decimal-and-hex-codes/)
The University of Victoria's linguistics department provides a helpful guide on using the IPA. It also mentions the use of the period to denote syllable boundaries: "A period is used to mark the boun