I've been in Germany for a couple of months now and of course there the obvious signs you're not a local when you open your mouth.
Here are couple of other subtle ones I'm noticing:
- I'm so used to putting my left foot down on the curbside when stopping on my bike I can't stop now I'm riding on the right. Hardly anyone else does that.
- Germans wear their wedding rings on their right hands, we wear them on the left.
This list will update over time, keep checking back!