Siddhi means accomplishment.
First, a bit of background: Please tell us what your TM practise consisted of - just TM 2x20 or more than that? how long did you do TM? did you use "advanced" techniques? supplements? TMSP? Please tell us what details you are comfortable discussing. Then: On this basis, can you tell us what have you accomplished as a result of your TM practise.
Were your TM accomplishments positive for you? negative for you? positive for others? negative for others?
Were you able to observe any kind of directly-TM-related accomplishment(s) in others also doing some aspect of Mahesh's TM program? If you are looking back to former times, what do you think of these accomplishment(s) now? Is it possible they were "real" or something else? (What?)
As William has suggested: what do you think Mahesh/the TM organization has accomplished? in what terms do you think these accomplishment(s) can best be quantified or categorized?
Perhaps you have since TM practised something else. If you want, can you tell us something about what you feel is your accomplishment outside the boundaries of TM?