How to put a marker on a specific bar

plotshape takes a condition as its first argument and marks the bars where it holds. To mark one bar, write a condition that is true on one bar.

plotshape(series bool series, const string title, input shape shape, input location location, series color color, input int offset, const string text, series color textcolor, input size size, const bool force_overlay) → void

indicator("Mark the last bar", "lastbar", true)
plot(close, title = "Close", color = color.gray)
plotshape(barstate.islast, title = "Last bar", shape = shape.flag, location = location.abovebar, color = color.blue, size = size.small)

Choosing the condition

bar_index is a series int, so it changes bar by bar and a comparison against it picks out one bar.

If you want a character rather than a shape

Use plotchar. It takes the same arguments with char in place of shape. Pass one character: a longer string is cut to its first character, with no warning and no error.

If the mark’s size should follow a measured value

Use plotarrow, which takes a number rather than a condition. It has no location, no shape, no size and no text — where the arrow sits follows from the number you give it.

If the mark should sit beside the bar rather than on it

offset shifts it. The parameter is input-form, so one fixed shift applies to every mark; it cannot vary from bar to bar.

The failure to watch for

All three functions must be called at the top level. Two conditions mean two calls, not one call inside a branch.

See Text and markers.