Fr Ray Blake has a post on his blog about the external marks by which Catholics were, at one time, easily recognised. The implication is that nowadays most of these practices are rarely seen.
Here is a list, mostly taken from Fr Blake's blog:
Corpus Christi and Marian Processions,
The religious life,
Kneeling in church,
Reception of Holy Communion on the tongue,
Crucifixes in the home,
Blessing oneself with holy water when entering a church,
Making the sign of the cross when passing a church.
What prompted this discussion was the welcome proposal of the bishops of England and Wales to re-introduce Friday abstinence. The list suggests plenty more customs and practices that could be revived.