A common and useful way to tag posts on tumblr. The 'ts' stands for 'tumblr savior', a third party app which lets users hide posts which contain certain words or phrases. If someone is tagging with a word (or phrase) followed by 'for ts', they are making sure that followers who have the word 'saviored' will not see their post, while also preventing their post from appearing on the larger (and often much more cluttered) tag that exists for the word itself.
'#glee for ts' rather than '#glee'
'#teen wolf for ts' rather than '#teen wolf'