From Max Black's Companion, Wittgenstein provides an example a couple sections later (boldface my own):
3.344 What signifies in a symbol is what is common to all the symbols that the rules of logical syntax allow us to substitute for it.
3.3441 For instance, we can express what is common to all notations for truth-functions in the following way: they have in common that, for example, the notation that uses 'Pp' ('not p') and 'p C g' ('p or g') can be substituted for any of them. (This serves to characterize the way in which something general can be disclosed by the possibility of a specific notation.)
3.3442 Nor does analysis resolve the sign for a complex in an arbitrary way, so that it would have a different resolution every time that it was incorporated in a different proposition.
3.4 A proposition determines a place in logical space. The existence of this logical place is guaranteed by the mere existence of the constituents—by the existence of the proposition with a sense.
3.41 The propositional sign with logical coordinates—that is the logical place.
3.411 In geometry and logic alike a place is a possibility: something can exist in it.
Consider as well the following passages:
2.033 Form is the possibility of structure.
5.4711 To give the essence of a proposition means to give the essence of all description, and thus the essence of the world.