I seen several things recently that makes me believe this is already possible. When the Mabar event was enabled, there was a notification of this when you logged in. Also, yesterday, after the downtime, upon log in, there was a message about ship buffs needing possibly an hour to repopulate.
So my suggestion is this. When there is a bonus weekend, would it be possible to have some sort of notification? For instance, this weekend was a +2 loot weekend, so something like : Get Looting, +2 loot now active, or some such upon logging in?
Not everyone reads the forums and the bonus weekends aren't always advertised in the launcher.