"Teacheth my hands to war, and my fingers to fight"

There are many things that Old Believers see as Apostolic tradition. Even though this is quite often not the case, many of their practices are in fact at least Byzantine in origin and thus, are part of the overall Eastern Christian heritage. There is no reason, why these should be viewed as specifically Old Believer (as part of  a specific ethno-religious culture) and not just "Eastern" or at least Byzantine. Moreover, some practices can even be viewed as Chrisian in general. We'll start by showcasing just one of such practices. 

Many have seen this gesture on various paintings:

I am not an art expert, so I am not going to go into semiotic analysis, but it seems that this gesture symbolises humility ("broken spirit" of Ps. 50/51), feeling of unworthiness or gratitude. However, according to the Old Believers (and, presumably, pre-1666 Russian and, at a certain period, Byzantine Church) this gesture is not just something depicted on paintings or icons, it is the way a Christian is supposed to hold his\her hands at all times when praying in a church. The ideal way to hold hands is much like on the paintings above and much like Byzantine-rite Christians hold their hands when approaching the Holy Communion:

One can even see this gesture in action on Western miniatures:

This is supposed to imitate the cherubim and has more to do with sacred fear or being collected for prayer. However, it is quite difficult to stand that way the whole service, especially considering how long the services are when one follows the Jerusalem Typikon to the dot. Though it should be mentioned that a Wanderer Old Believer (strannyk) told me that their faithful stand like that the whole service. But anyway, there is a more comfortable position that became much more popular:

This also reminds me of the way some saints are depicted in Western art, for instance this satue of Saint Bruno (who is usually depicted with hands crossed on the chest):

Unforetunately, some forget the meaning of this gesture and as a result, some Old Believer churches resemble a gathering of security tough guys, waiting to whale on a Nikonian, who will walk in by accident. Perhaps this is a trivial custom but it might be helpful to some. By the way, the last time the question of where to hold one's hands was revisited by Ignatius Brianchaninov, who thought it was better to just hold one's hands like a soldier, keeping them at our sides.