PAY ATTENTION
I recently received a response from a colleague that stated they did not know what my email message was all about.
My response was for him to read the Subject line and it would immensely become clear as a bell.
Pure as the sound of a bell; also, readily understood. For example, Did you understand the message I left you? —Yes, clear as a bell . This simile, which alludes to the bell's clarity owing to lack of overtones, was already a proverb in John Ray's English Proverbs (1670).