So that above image was just tweeted by Isaiah Thomas today, February 20th. The only other time he sent out a message as cryptic or oddly specific as that was on July the 2nd here:
And that was immediately followed by the Al Hoford announcement.
The Celtics have been rumored to be involved in a number of trades over the past three seasons, but the one currently with the most steam behind it is the one involving Jimmy Butler of Chicago moving in. Paul George was seemingly an option, but those rumored has since died down due to the Pacers saying all the right things in the front office.
Boston has a variety of trade assets, including a lot of future Nets lottery picks at their disposal.