Hi there,
Welcome to SeaTheme forum.

It is possible by custom CSS(“Appearance > Customize: Additional CSS”), like:

.menu-item-has-children > a:after {
    content: '';
    display: inline-block;
    width: 4px;
    height: 4px;
    border-radius: 0;
    margin-left: 4px;
    background-color: transparent;
    background-repeat: no-repeat;
    background-size: contain;
    background-image: url(indicator-icon-image-url);
}

The indicator-icon should be a image(png, jpg or gif) file, it should be uploaded your website then get the image URL. Replace indicator-icon-image-url of background-image as the image URL(should be like http://www.abc.com/image.png)

Regards!
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