I noticed that there is a tendency to have a house rule allowing Tremere to have a second Magical Focus in addition to their MMF in Certamen (or to allow a different house virtue), because otherwise the MMF in Certamen "occupies" the only Magical Focus you can have with a sub-par one.
There is, however, another point that makes the house Tremere less attractive: In 4e, No Sigil was a required minor (1 point) flaw for Tremere magi. In 5e, Tremere still don't hold their own sigils until they beat their parens in certamen (or until the parens dies), but now it's a "free flaw" for which they don't get anything back. The other two houses that have some drawbacks are Bjornaer (cannot have familiars) and Verditius (require casting tools), but they get something much better in return.
It seems that holding your own sigil as a Tremere is unusual:
-In the Stonehenge, Normandy, Provencal, and Theban tribunals, only one Tremere sigil holder is described (usually with language allowing for more in your own saga). The Rhine has two, while Hibernia does not even have a single one.
-In order to become a Master in the Rhine tribunal, which usually happens 30-40 years after gauntlet, control over one’s own sigil is not required (but it helps).
That indicates to me that you probably shouldn't try to challenge your parens in your first 30 years post Gauntlet. Maybe it's just considered inappropriate.
What are the implications of that?
-Technically, the parens holding the sigil is just a permanent free proxy. I would still guess that not holding your sigil means that you might be viewed as less than a full magus by other houses (although if only a small minority of Tremere hold their sigils, that may relativize this view as there are evidently very capable magi that don't hold their sigil).
-In Stonehenge, there is a roll call at the start of each tribunal, where each mage is asked to confirm that they have a voting sigil (p. 116). That means that Tremere cannot even attend a tribunal.
Something positive that Tremere get as part of their house is support. The box on p. 120 makes it clear that this is supposed to balance out the seasons of study they lose while carrying out their duties so they advance at a similar speed to other magi. It is definitely not intended to balance the no sigil point, as there is more support for higher-ranking magi, who are more likely to already have claimed their sigil.
I understand that the whole sigil issue is used to emphasize the focus of the house on hierarchy and unity, but it still seems like a drawback. Is there a way to balance it?
Making it a mandatory flaw as in 4e might be too much. I don't think it rises to the level of other hermetic flaws. Looking at flaws that don't directly impact casting, Hedge Wizard and Infamous Master give you a negative hermetic reputation. This can be quite punishing (rightfully so, considering the balance with other minor hermetic flaws).
Could there be some house flavor that balances the no sigil flavor? Maybe just the amount of duties you have to perform?