this is a motto or aphorism, to guess from the circumstances of my coming across it, but, from the rural fastnesses of northern New England, I don't know how to find out what language is involved. If it is an accepted invented language, it may have borrowed elements that living languages developed for their own use (beside the obvious Roman letters). the "si" word perhaps connotes a conditional or an affirmative ['if' or 'yes'], and the '-is' could be second person singular verb forms. That, however, is rank speculation and doesn't solve the problem. Over to you kind experts!