How would it be enforced? Easy. Show some third parties a timeline of rsync's social media posting before, and after the court order. Remove the absolute time data and don't tell them which is before and which is after.
If they (the overwhemling majority of third parties to which this is shown) can correctly distinguish them better than chance, then rsync was trying violating the anti-tipoff order.
Incidentally, what I just described is basically the test for whether a cryptosystem is "semantically secure", which is often expected.
rsync's lawyers could argue that the sampling sizes were far to small for the trends claimed to have any significance, arguing that any discrepancy could easily be explained by a lack of good opportunities to bring it up.
The court could order it, and they could try to enforce it, but unlike "don't send an email to your mother about this" (which is a rather concrete thing) it would be very messy and wishy-washy. In perhaps the worse case scenario for the court, they would have to deal with figuring out how to measure "enthusiasm". Do rsync's posts seem more dejected these days? Is that just the court's bias showing, or is dejection measurable in some sort of objective/empirical way?
If they (the overwhemling majority of third parties to which this is shown) can correctly distinguish them better than chance, then rsync was trying violating the anti-tipoff order.
Incidentally, what I just described is basically the test for whether a cryptosystem is "semantically secure", which is often expected.