My understanding is - and my internet-research reassured me - that one uses lower-case letters for the probability density function and upper-case letters for absolute probabilities. 'p' vs 'Pr' for example.
Now, I'm reading an established textbook ("Computer Vision: Models, Learning, and Inference" the PDF-textfile is available here: http://www.computervisionmodels.com/) and the author uses 'Pr' to notate probability density functions. See bottom of page 40 for example, where one can find the following formula:
Hence, I'm wondering whether this notation is common. Because I'm thinking about adapting it.