Do not confound thought with thinking. Thought is the Object that you think. Thinking, as contradistinguished from feeling and from the effort of attention, is the operation of the mind by which you strive to make out the Truth. You expect to extract it from the object before your mind, the Thought. That thought, then, is (or you hope it may be) a Sign of the Truth. Thought then is a Sign.
http://www.commens.org/dictionary/entry/quote-system-existential-graphs-considered-instrument-investigation-logic-14