Hi there, Futi. Commas and periods are considered special characters.
Although these are deemed as one, they're still acceptable characters. Since you're converting your QuickBooks Desktop Mac to Windows, you'll need to removed any memos that are longer than 50 characters and if they contain the following symbols: !@#$%^&*
For reference, read Step 2 of this article: Move QuickBooks for Mac file to QuickBooks for Windows.
You can also view this website to get your hands on other helpful resources in QBDT: Self-help articles.
I'll be around the corner to help if you have further questions about accepted special characters in QBDT. Have a great day!