The three geometric shapes represent principles of movement and thought. Not related to the word aikido at all.
Here's an interesting tidbit. Look carefully at the Japanese character for "ai" or harmony. You will see a roof over a square representing a mouth or house. Also there is the dash for "one".
all together this is - "under this roof we speak with one voice" or harmony.
related to the characters, though.
in the context of kanji. Abe Sensei's work may be of some light.