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.
Per the Glose, the three lines in the upper portion represent the concept of 'many'. The lower portion of the symbol represents 'mouth'. Thus, 'three (many) mouths speaking together'.