One thing I've noticed as a string player within an orchestra (cellist), is the range of clapping within the string players (though some of you wind and percussion players do this too), mainly for soloists (either in concerti or within the orchestra body itself), but also for other items within that concert.

Generally, there are three main stages of clapping tecniques-
1. Hitting their leg with one hand - this leg is generally on the audience's side, especially if said string player is on the edge of the orchestra, next to the audience. This makes it public that they are clapping and appreciate the hard work etc. etc..

2. Clapping with both hands, one of which is still holding the bow - this can be difficult, but very often musicians can't be bothered to put the bow down. However, this stage shows more appreciation and praise than just hitting their leg.

3. When the soloist performed exceptionally well, it can be necessary to put the bow down and clap with both hands properly. This stage is rare, but extremely rewarding.

I don't know if anyone else has noticed this.

I often clap my hand against my thigh, but I think that the most common substitute for clapping is to move ones bow up and down

Really? I've never seen that!
Thigh slapping actually generates some kind of appreciative sound as well as just looking appreciative, while claping avec bow can be rather unwieldy...

In Australia players are more likely to shuffle or stamp their feet in appreciation. Are we the only country that does this?! I just assumed everyone did!

Well at Freddy Kempf's Bach recital I went to last week in Leeds the entire audience was stamping feet as well as clapping !

I would have said that Japanese string players just sit there but that's not true.

The major orchestra is also a broadcasting orchestra, and most of their live concerts are recorded and broadcast later, so no doubt they are not encouraged to catcall, howl, stamp, etc...

Celloists and violinists seem to either tap their LH fingers on the fingerboard with an open/close movement, or tap their RH fingers over their LH (not with the violin under the chin, of course).

But the most common acknowledgement appears to be the "bow-waggle"! Place your RH fist on your knee, clutching your bow, and waggle the tip back and forth. Got it?

Violists are, naturally, invisible behind the conductor or soloist !