For those unfamiliar with Usenet abbreviations, "tin-" and "tan-" in brackets (and, often, smaller lettering), refer to "there is no..." and "there are no...", respectively. These are followed by the initials of whatever was just mentioned and is now being nullified.
For example, in the statement "Poetry audiences (tanpa) love me!" the "tanpa" reminds readers that there are no poetry audiences in real life. Similarly, having read "on the demand side (tinds) of poetry", an unsuspecting newcomer would be warned by "tinds" that there is no demand side for poetry.