Pictograms are used on Reader much like emoticons are used elsewhere. In general, symbols may be repeated to express greater intensity (see reduplication).
+ Used to applaud a comment or note that is especially funny or observant.
R Ironic replacement for + in the wake of Google's announcement to move social functions from Google Reader to Google Plus.
- Used to express negative feelings about a comment or note
^ When followed by a comment, used to indicate the position of the comment one is responding to; the number of repetitions refers to the number of positions above one's one comment. (Thus, ^^^ [comment] would answer a comment three positions higher.) When used alone, it is generally understood as a symbol of approval for the comment immediately above it.
@ Used to direct a comment or note to a specific person or group
:) As seen elsewhere, used to denote happiness
:( As seen elsewhere, used to denote sadness
:/ As seen elsewhere, used to denote general discomfort or dread. Often used as a response to discussions of misery that one applauds but does not want to Like. (See also: -_-).
-_- As seen elsewhere, used to denote dissatisfaction or defeat. Often used as a response to some kind of onerous task or a regrettable social situation. (See also: :/ )
<3 Represents a heart, used to express affection or approval. Often used to bump a share.
(_I_) Represents human buttocks, used to express disapproval or general ridiculousness. Often used when a comment thread devolves into a fight.
( See also: 8===D~~)
8===D~~ Represents a human phallus (a fact which must often be explained to newcomers). Often used when a comment thread devolves into a fight. ( See also: (_I_) ).
¯\_(ツ)_/¯ - A reference to the famed Sandusky Shrug. Used to denote an ironic "oh well". Two backslashes are required in the left arm for it to appear properly.