Allows a user to create custom markers in maya.Based off of this pastebin: http://pastebin.com/Uc8S4QPx (which may further be from createive Crash) and further work by https://github.com/achayan and his pasteBin http://pastebin.com/JGJZ5uu1

mayaCustomMarkers.py

from PyQt4 import QtGui, QtCore
import maya.cmds as cmds
import maya.OpenMayaUI as mui
import sip

def convertToQT(controlName):
    controlPoniter = mui.MQtUtil.findControl(controlName)
    if controlPoniter is not None:
        return sip.wrapinstance(long(controlPoniter), QtCore.QObject)

def getTimeline():
    qtTimeline = convertToQT("timeControl1")
    return qtTimeline

def getTimelineRange():
    r = cmds.timeControl("timeControl1", query=True, ra=True)
    return range(int(r[0]), int(r[1]))

class Markers(QtGui.QWidget):
    def __init__(self, timeline=getTimeline()):
        super(Markers, self).__init__(timeline)
        layout = timeline.layout()
        if not layout:
            layout = QtGui.QVBoxLayout(timeline)
            layout.setContentsMargins(0, 0, 0, 0)
            timeline.setLayout(layout)
        else:
            for child in timeline.children():
                if child.objectName() == "timelineMarkers":
                    child.deleteLater()
        layout.addWidget(self)
        self.setObjectName("timelineMarkers")
        self.start  = None
        self.end    = None
        self.total  = None
        self.step   = None
        self.frames = []
        self.colors = []
        self.update()

    def paintEvent(self, event):
        self.draw()

    def add(self):
        color=[255, 0, 0]
        for f in getTimelineRange():
            if not f in self.frames:
                self.frames.append(f)
                self.colors.append(color)
            else:
                index = self.frames.index(f)
                self.colors[index]   = color
        self.update()

    def draw( self ):
        self.start = cmds.playbackOptions(query=True, min=True)
        self.end   = cmds.playbackOptions(query=True, max=True)
        self.total = self.width()
        self.step  = (self.total - (self.total * 0.01)) / (self.end - self.start + 1)
        if not self.frames or not self.colors:
            return
        painter = QtGui.QPainter(self)
        pen = QtGui.QPen()
        pen.setWidth(self.step)
        for f, c in zip(self.frames, self.colors):
            color = QtGui.QColor('#fbc02d')
            color.setAlpha(50)
            pen.setColor(color)
            pos  = (f - self.start + 0.5) * self.step + (self.total * 0.005)
            line = QtCore.QLineF(QtCore.QPointF(pos, 0), QtCore.QPointF(pos, 100))
            painter.setPen(pen)
            painter.drawLine(line)
            
def addMark():
    global markers
    try:
        print markers
        assert markers
    except:
        markers=Markers()
    markers.add()
addMark()