In order to have a left arm on ¯_(ツ)_/¯ you need to use triple \, like this: ¯\\\_(ツ)_/¯.

1. \ by default tells markdown to not turn _ into italics, so it displays _, but not \.
2. In \\, the first \ tells markdown that the second \ is not interacting with _ but is a standalone thing. However, markdown now thinks that _ is italics.
3. That's what the third \ is for. First \ allows second \, and the third \ allows _.

¯_(ツ)/¯ = ¯\_(ツ)_/¯
¯\(ツ)_/¯ = ¯\\_(ツ)_/¯
¯\_(ツ)_/¯ = ¯\\\_(ツ)\_/¯