<Tr> <Td> Ë </Td> <Td> Alt + 0203 </Td> <Td> Alt + 211 </Td> </Tr> <Tr> <Td> Ï </Td> <Td> Alt + 0207, Alt + 02255 </Td> <Td> Alt + 216 </Td> </Tr> <Tr> <Td> Ö </Td> <Td> Alt + 0214 </Td> <Td> Alt + 153 </Td> </Tr> <Tr> <Td> Ü </Td> <Td> Alt + 0220 </Td> <Td> Alt + 154 </Td> </Tr>

What do the two little dots over a letter mean