Why is this 'eject' icon showing next to my drive?

I'm new to ubuntu world and just freshly installed ubuntu 16.04 on my system.But I don't why is this symbol showing.

So why is there unmounting symbol showing? Is it normal or I have misplaced some step during installation?

I have previously installed windows 8.1 on my system. So Computer directory is in place of Local disk c and media and software are "local disk D and E".

Here is the output of lsblk -a:

That button gives you an easy way to unmount the partition. It is 'normal'.

In this case unmounting is not the same as ejecting a USB device or a DVD disk. After unmounting the device is still powered and can be mounted again. After ejecting a USB pendrive, it is powered off, and must be unplugged and plugged in to be mounted again.

You may want to unmount a device to protect it from reading and/or writing, even when it is still connected (and in this case there are two such partitions on the same 1 TB hard disk drive as the running operating system).

I've posted a couple of comments already so I'll just wrap them up with an answer and a picture:

The first Eject button is for the Android phone.

Below that we have:

• "Computer" the mounted Linux partition on 120 GB mSata SSD /dev/sdc3
• "KSX_Win7" Kingston Savage X 240 GB SSD /dev/sda2 (Unmounted)
• "KSX Win 8.1" Kingston Savage X 240 GB SSD /dev/sda3 (Unmounted)
• "ST9_Linux" Seagate Technologies 512 GB HDD /dev/sdb5 (Unmounted)
• "ST9_Win7" Seagate Technologies 512 GB HDD /dev/sdb2 (Mounted)
• "Music" bookmark into ST9_Win7/Users/Person/Music/iTunes/iTunesMedia/Music

As you can see bookmarks are handy to save you a lot of clicking during drill down.

The design of Nautilus is to always show you partitions you can mount by clicking on their name. After clicking the partition name the "Eject" icon appears. Clicking "Eject" simply unmounts the partition.

If you want to hide a partition from Nautilus use the Disks application (How do I hide / remove a partition from the Nautilus left panel?). For example in the above Nautilus screen the partition /dev/sdc2 - F9m_Win7 has been hidden using the Disks application. The reason was it's a brand new install and broken so not much point in having it appear in Nautilus.

The entire lsblk is:

NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sda      8:0    0 223.6G  0 disk 
├─sda1   8:1    0   100M  0 part 
├─sda2   8:2    0  69.1G  0 part 
├─sda3   8:3    0  58.6G  0 part 
└─sda4   8:4    0     1K  0 part 
sdb      8:16   0 465.8G  0 disk 
├─sdb1   8:17   0   100M  0 part 
├─sdb2   8:18   0 257.4G  0 part /media/rick/ST9_Win7
├─sdb3   8:19   0     1K  0 part 
├─sdb5   8:21   0 200.5G  0 part 
└─sdb6   8:22   0   7.9G  0 part 
sdc      8:32   0 119.2G  0 disk 
├─sdc2   8:34   0  58.6G  0 part /mnt/5824BF4E76D68BE2
├─sdc3   8:35   0  29.3G  0 part /
└─sdc4   8:36   0   7.8G  0 part [SWAP]
sr0     11:0    1 695.9M  0 rom  

In summary Nautilus gives us a nice GUI into our partitions. It's very handy on this Laptop with three drives and many partitions.

Those are your sda(hdd) partitions that mounted automatically under /media. Those icons are actually notifying that those partitions can be unmounted.