Hold thumbs
Definition 1 of 1
Pro Tip 1/3Good Luck Gesture
In South Africa, 'hold thumbs' means the same as 'crossing fingers' and is a way to wish good luck. 
She's taking her driving test today, so I'm holding thumbs.
Pro Tip 2/3Positive Support
'Hold thumbs' is used to show support and optimism towards someone's situation or outcome. 
We're holding thumbs that the weather stays clear for the picnic.
Pro Tip 3/3Informal Use
The phrase is informal, so it's best used with friends, family, or casual settings, not in formal situations. 
Got a job interview? I'll hold thumbs for you!