Sentence:  In order that they might represent the worlds of experience and imagination, such symbols have to be put together with ‘<WSD>indexical</WSD>' signs, as Peirce termed them, such as articles (the, some), demonstratives (this, those), tense-inflections (walk-s, walk-ed), moods (may/might walk, shall/should walk) etc. 
Meaning of the word marked with <WSD> tags:  Having the character of pointing to, or indicating, a particular state of affairs.