What is the notation about group differences in terms standard deviations?
The psychology notation for standardized differences between group means is d. I.e., the difference between group differences divided by the within-group standard deviation. Note that there are some variants about which group is used or whether a pooled standard deviation is obtained.

I.e., in your example: d = 0.3.

If you want to report means and sds, then you typically use M and SD.